fast-diff - npm Package Compare versions

Comparing version 1.1.2 to 1.2.0

diff.js

@@ -42,8 +42,8 @@ /**
  * @param {string} text2 New string to be diffed.
- * @param {Int} cursor_pos Expected edit position in text1 (optional)
+ * @param {Int|Object} [cursor_pos] Edit position in text1 or object with more info
  * @return {Array} Array of diff tuples.
  */
-function diff_main(text1, text2, cursor_pos) {
-  // Check for equality (speedup).
-  if (text1 == text2) {
+function diff_main(text1, text2, cursor_pos, _fix_unicode) {
+  // Check for equality
+  if (text1 === text2) {
     if (text1) {
@@ -55,5 +55,7 @@ return [[DIFF_EQUAL, text1]];
 
-  // Check cursor_pos within bounds
-  if (cursor_pos < 0 || text1.length < cursor_pos) {
-    cursor_pos = null;
+  if (cursor_pos != null) {
+    var editdiff = find_cursor_edit_diff(text1, text2, cursor_pos);
+    if (editdiff) {
+      return editdiff;
+    }
   }
@@ -83,7 +85,3 @@
   }
-  diff_cleanupMerge(diffs);
-  if (cursor_pos != null) {
-    diffs = fix_cursor(diffs, cursor_pos);
-  }
-  diffs = fix_emoji(diffs);
+  diff_cleanupMerge(diffs, _fix_unicode);
   return diffs;
@@ -116,7 +114,9 @@ };
   var i = longtext.indexOf(shorttext);
-  if (i != -1) {
+  if (i !== -1) {
     // Shorter text is inside the longer text (speedup).
-    diffs = [[DIFF_INSERT, longtext.substring(0, i)],
-             [DIFF_EQUAL, shorttext],
-             [DIFF_INSERT, longtext.substring(i + shorttext.length)]];
+    diffs = [
+      [DIFF_INSERT, longtext.substring(0, i)],
+      [DIFF_EQUAL, shorttext],
+      [DIFF_INSERT, longtext.substring(i + shorttext.length)]
+    ];
     // Swap insertions for deletions if diff is reversed.
@@ -129,3 +129,3 @@ if (text1.length > text2.length) {
 
-  if (shorttext.length == 1) {
+  if (shorttext.length === 1) {
     // Single character string.
@@ -185,3 +185,3 @@ // After the previous speedup, the character can't be an equality.
   // with the reverse path.
-  var front = (delta % 2 != 0);
+  var front = (delta % 2 !== 0);
   // Offsets for start and end of k loop.
@@ -198,3 +198,3 @@ // Prevents mapping of space beyond the grid.
       var x1;
-      if (k1 == -d || (k1 != d && v1[k1_offset - 1] < v1[k1_offset + 1])) {
+      if (k1 === -d || (k1 !== d && v1[k1_offset - 1] < v1[k1_offset + 1])) {
         x1 = v1[k1_offset + 1];
@@ -205,4 +205,6 @@ } else {
       var y1 = x1 - k1;
-      while (x1 < text1_length && y1 < text2_length &&
-             text1.charAt(x1) == text2.charAt(y1)) {
+      while (
+        x1 < text1_length && y1 < text2_length &&
+        text1.charAt(x1) === text2.charAt(y1)
+      ) {
         x1++;
@@ -220,3 +222,3 @@ y1++;
         var k2_offset = v_offset + delta - k1;
-        if (k2_offset >= 0 && k2_offset < v_length && v2[k2_offset] != -1) {
+        if (k2_offset >= 0 && k2_offset < v_length && v2[k2_offset] !== -1) {
           // Mirror x2 onto top-left coordinate system.
@@ -236,3 +238,3 @@ var x2 = text1_length - v2[k2_offset];
       var x2;
-      if (k2 == -d || (k2 != d && v2[k2_offset - 1] < v2[k2_offset + 1])) {
+      if (k2 === -d || (k2 !== d && v2[k2_offset - 1] < v2[k2_offset + 1])) {
         x2 = v2[k2_offset + 1];
@@ -243,5 +245,6 @@ } else {
       var y2 = x2 - k2;
-      while (x2 < text1_length && y2 < text2_length &&
-             text1.charAt(text1_length - x2 - 1) ==
-             text2.charAt(text2_length - y2 - 1)) {
+      while (
+        x2 < text1_length && y2 < text2_length &&
+        text1.charAt(text1_length - x2 - 1) === text2.charAt(text2_length - y2 - 1)
+      ) {
         x2++;
@@ -259,3 +262,3 @@ y2++;
         var k1_offset = v_offset + delta - k2;
-        if (k1_offset >= 0 && k1_offset < v_length && v1[k1_offset] != -1) {
+        if (k1_offset >= 0 && k1_offset < v_length && v1[k1_offset] !== -1) {
           var x1 = v1[k1_offset];
@@ -311,3 +314,3 @@ var y1 = v_offset + x1 - k1_offset;
   // Quick check for common null cases.
-  if (!text1 || !text2 || text1.charAt(0) != text2.charAt(0)) {
+  if (!text1 || !text2 || text1.charAt(0) !== text2.charAt(0)) {
     return 0;
@@ -322,4 +325,6 @@ }
   while (pointermin < pointermid) {
-    if (text1.substring(pointerstart, pointermid) ==
-        text2.substring(pointerstart, pointermid)) {
+    if (
+      text1.substring(pointerstart, pointermid) ==
+      text2.substring(pointerstart, pointermid)
+    ) {
       pointermin = pointermid;
@@ -332,2 +337,7 @@ pointerstart = pointermin;
   }
+
+  if (is_surrogate_pair_start(text1.charCodeAt(pointermid - 1))) {
+    pointermid--;
+  }
+
   return pointermid;
@@ -345,4 +355,3 @@ };
   // Quick check for common null cases.
-  if (!text1 || !text2 ||
-      text1.charAt(text1.length - 1) != text2.charAt(text2.length - 1)) {
+  if (!text1 || !text2 || text1.slice(-1) !== text2.slice(-1)) {
     return 0;
@@ -357,4 +366,6 @@ }
   while (pointermin < pointermid) {
-    if (text1.substring(text1.length - pointermid, text1.length - pointerend) ==
-        text2.substring(text2.length - pointermid, text2.length - pointerend)) {
+    if (
+      text1.substring(text1.length - pointermid, text1.length - pointerend) ==
+      text2.substring(text2.length - pointermid, text2.length - pointerend)
+    ) {
       pointermin = pointermid;
@@ -367,2 +378,7 @@ pointerend = pointermin;
   }
+
+  if (is_surrogate_pair_end(text1.charCodeAt(text1.length - pointermid))) {
+    pointermid--;
+  }
+
   return pointermid;
@@ -407,10 +423,10 @@ };
     var best_longtext_a, best_longtext_b, best_shorttext_a, best_shorttext_b;
-    while ((j = shorttext.indexOf(seed, j + 1)) != -1) {
-      var prefixLength = diff_commonPrefix(longtext.substring(i),
-                                           shorttext.substring(j));
-      var suffixLength = diff_commonSuffix(longtext.substring(0, i),
-                                           shorttext.substring(0, j));
+    while ((j = shorttext.indexOf(seed, j + 1)) !== -1) {
+      var prefixLength = diff_commonPrefix(
+        longtext.substring(i), shorttext.substring(j));
+      var suffixLength = diff_commonSuffix(
+        longtext.substring(0, i), shorttext.substring(0, j));
       if (best_common.length < suffixLength + prefixLength) {
-        best_common = shorttext.substring(j - suffixLength, j) +
-            shorttext.substring(j, j + prefixLength);
+        best_common = shorttext.substring(
+          j - suffixLength, j) + shorttext.substring(j, j + prefixLength);
         best_longtext_a = longtext.substring(0, i - suffixLength);
@@ -423,4 +439,6 @@ best_longtext_b = longtext.substring(i + prefixLength);
     if (best_common.length * 2 >= longtext.length) {
-      return [best_longtext_a, best_longtext_b,
-              best_shorttext_a, best_shorttext_b, best_common];
+      return [
+        best_longtext_a, best_longtext_b,
+        best_shorttext_a, best_shorttext_b, best_common
+      ];
     } else {
@@ -432,7 +450,5 @@ return null;
   // First check if the second quarter is the seed for a half-match.
-  var hm1 = diff_halfMatchI_(longtext, shorttext,
-                             Math.ceil(longtext.length / 4));
+  var hm1 = diff_halfMatchI_(longtext, shorttext, Math.ceil(longtext.length / 4));
   // Check again based on the third quarter.
-  var hm2 = diff_halfMatchI_(longtext, shorttext,
-                             Math.ceil(longtext.length / 2));
+  var hm2 = diff_halfMatchI_(longtext, shorttext, Math.ceil(longtext.length / 2));
   var hm;
@@ -472,4 +488,5 @@ if (!hm1 && !hm2) {
  * @param {Array} diffs Array of diff tuples.
+ * @param {boolean} fix_unicode Whether to normalize to a unicode-correct diff
  */
-function diff_cleanupMerge(diffs) {
+function diff_cleanupMerge(diffs, fix_unicode) {
   diffs.push([DIFF_EQUAL, '']);  // Add a dummy entry at the end.
@@ -483,4 +500,9 @@ var pointer = 0;
   while (pointer < diffs.length) {
+    if (pointer < diffs.length - 1 && !diffs[pointer][1]) {
+      diffs.splice(pointer, 1);
+      continue;
+    }
     switch (diffs[pointer][0]) {
       case DIFF_INSERT:
+
         count_insert++;
@@ -496,16 +518,59 @@ text_insert += diffs[pointer][1];
       case DIFF_EQUAL:
-        // Upon reaching an equality, check for prior redundancies.
-        if (count_delete + count_insert > 1) {
-          if (count_delete !== 0 && count_insert !== 0) {
-            // Factor out any common prefixies.
+        var previous_equality = pointer - count_insert - count_delete - 1;
+        if (fix_unicode) {
+          // prevent splitting of unicode surrogate pairs.  when fix_unicode is true,
+          // we assume that the old and new text in the diff are complete and correct
+          // unicode-encoded JS strings, but the tuple boundaries may fall between
+          // surrogate pairs.  we fix this by shaving off stray surrogates from the end
+          // of the previous equality and the beginning of this equality.  this may create
+          // empty equalities or a common prefix or suffix.  for example, if AB and AC are
+          // emojis, `[[0, 'A'], [-1, 'BA'], [0, 'C']]` would turn into deleting 'ABAC' and
+          // inserting 'AC', and then the common suffix 'AC' will be eliminated.  in this
+          // particular case, both equalities go away, we absorb any previous inequalities,
+          // and we keep scanning for the next equality before rewriting the tuples.
+          if (previous_equality >= 0 && ends_with_pair_start(diffs[previous_equality][1])) {
+            var stray = diffs[previous_equality][1].slice(-1);
+            diffs[previous_equality][1] = diffs[previous_equality][1].slice(0, -1);
+            text_delete = stray + text_delete;
+            text_insert = stray + text_insert;
+            if (!diffs[previous_equality][1]) {
+              // emptied out previous equality, so delete it and include previous delete/insert
+              diffs.splice(previous_equality, 1);
+              pointer--;
+              var k = previous_equality - 1;
+              if (diffs[k] && diffs[k][0] === DIFF_INSERT) {
+                count_insert++;
+                text_insert = diffs[k][1] + text_insert;
+                k--;
+              }
+              if (diffs[k] && diffs[k][0] === DIFF_DELETE) {
+                count_delete++;
+                text_delete = diffs[k][1] + text_delete;
+                k--;
+              }
+              previous_equality = k;
+            }
+          }
+          if (starts_with_pair_end(diffs[pointer][1])) {
+            var stray = diffs[pointer][1].charAt(0);
+            diffs[pointer][1] = diffs[pointer][1].slice(1);
+            text_delete += stray;
+            text_insert += stray;
+          }
+        }
+        if (pointer < diffs.length - 1 && !diffs[pointer][1]) {
+          // for empty equality not at end, wait for next equality
+          diffs.splice(pointer, 1);
+          break;
+        }
+        if (text_delete.length > 0 || text_insert.length > 0) {
+          // note that diff_commonPrefix and diff_commonSuffix are unicode-aware
+          if (text_delete.length > 0 && text_insert.length > 0) {
+            // Factor out any common prefixes.
             commonlength = diff_commonPrefix(text_insert, text_delete);
             if (commonlength !== 0) {
-              if ((pointer - count_delete - count_insert) > 0 &&
-                  diffs[pointer - count_delete - count_insert - 1][0] ==
-                  DIFF_EQUAL) {
-                diffs[pointer - count_delete - count_insert - 1][1] +=
-                    text_insert.substring(0, commonlength);
+              if (previous_equality >= 0) {
+                diffs[previous_equality][1] += text_insert.substring(0, commonlength);
               } else {
-                diffs.splice(0, 0, [DIFF_EQUAL,
-                                    text_insert.substring(0, commonlength)]);
+                diffs.splice(0, 0, [DIFF_EQUAL, text_insert.substring(0, commonlength)]);
                 pointer++;
@@ -516,28 +581,28 @@ }
             }
-            // Factor out any common suffixies.
+            // Factor out any common suffixes.
             commonlength = diff_commonSuffix(text_insert, text_delete);
             if (commonlength !== 0) {
-              diffs[pointer][1] = text_insert.substring(text_insert.length -
-                  commonlength) + diffs[pointer][1];
-              text_insert = text_insert.substring(0, text_insert.length -
-                  commonlength);
-              text_delete = text_delete.substring(0, text_delete.length -
-                  commonlength);
+              diffs[pointer][1] =
+                text_insert.substring(text_insert.length - commonlength) + diffs[pointer][1];
+              text_insert = text_insert.substring(0, text_insert.length - commonlength);
+              text_delete = text_delete.substring(0, text_delete.length - commonlength);
             }
           }
           // Delete the offending records and add the merged ones.
-          if (count_delete === 0) {
-            diffs.splice(pointer - count_insert,
-                count_delete + count_insert, [DIFF_INSERT, text_insert]);
-          } else if (count_insert === 0) {
-            diffs.splice(pointer - count_delete,
-                count_delete + count_insert, [DIFF_DELETE, text_delete]);
+          var n = count_insert + count_delete;
+          if (text_delete.length === 0 && text_insert.length === 0) {
+            diffs.splice(pointer - n, n);
+            pointer = pointer - n;
+          } else if (text_delete.length === 0) {
+            diffs.splice(pointer - n, n, [DIFF_INSERT, text_insert]);
+            pointer = pointer - n + 1;
+          } else if (text_insert.length === 0) {
+            diffs.splice(pointer - n, n, [DIFF_DELETE, text_delete]);
+            pointer = pointer - n + 1;
           } else {
-            diffs.splice(pointer - count_delete - count_insert,
-                count_delete + count_insert, [DIFF_DELETE, text_delete],
-                [DIFF_INSERT, text_insert]);
+            diffs.splice(pointer - n, n, [DIFF_DELETE, text_delete], [DIFF_INSERT, text_insert]);
+            pointer = pointer - n + 2;
           }
-          pointer = pointer - count_delete - count_insert +
-                    (count_delete ? 1 : 0) + (count_insert ? 1 : 0) + 1;
-        } else if (pointer !== 0 && diffs[pointer - 1][0] == DIFF_EQUAL) {
+        }
+        if (pointer !== 0 && diffs[pointer - 1][0] === DIFF_EQUAL) {
           // Merge this equality with the previous one.
@@ -567,11 +632,11 @@ diffs[pointer - 1][1] += diffs[pointer][1];
   while (pointer < diffs.length - 1) {
-    if (diffs[pointer - 1][0] == DIFF_EQUAL &&
-        diffs[pointer + 1][0] == DIFF_EQUAL) {
+    if (diffs[pointer - 1][0] === DIFF_EQUAL &&
+      diffs[pointer + 1][0] === DIFF_EQUAL) {
       // This is a single edit surrounded by equalities.
       if (diffs[pointer][1].substring(diffs[pointer][1].length -
-          diffs[pointer - 1][1].length) == diffs[pointer - 1][1]) {
+        diffs[pointer - 1][1].length) === diffs[pointer - 1][1]) {
         // Shift the edit over the previous equality.
         diffs[pointer][1] = diffs[pointer - 1][1] +
-            diffs[pointer][1].substring(0, diffs[pointer][1].length -
-                                        diffs[pointer - 1][1].length);
+          diffs[pointer][1].substring(0, diffs[pointer][1].length -
+            diffs[pointer - 1][1].length);
         diffs[pointer + 1][1] = diffs[pointer - 1][1] + diffs[pointer + 1][1];
@@ -581,8 +646,8 @@ diffs.splice(pointer - 1, 1);
       } else if (diffs[pointer][1].substring(0, diffs[pointer + 1][1].length) ==
-          diffs[pointer + 1][1]) {
+        diffs[pointer + 1][1]) {
         // Shift the edit over the next equality.
         diffs[pointer - 1][1] += diffs[pointer + 1][1];
         diffs[pointer][1] =
-            diffs[pointer][1].substring(diffs[pointer + 1][1].length) +
-            diffs[pointer + 1][1];
+          diffs[pointer][1].substring(diffs[pointer + 1][1].length) +
+          diffs[pointer + 1][1];
         diffs.splice(pointer + 1, 1);
@@ -596,171 +661,142 @@ changes = true;
   if (changes) {
-    diff_cleanupMerge(diffs);
+    diff_cleanupMerge(diffs, fix_unicode);
   }
 };
 
+function is_surrogate_pair_start(charCode) {
+  return charCode >= 0xD800 && charCode <= 0xDBFF;
+}
 
-var diff = diff_main;
-diff.INSERT = DIFF_INSERT;
-diff.DELETE = DIFF_DELETE;
-diff.EQUAL = DIFF_EQUAL;
+function is_surrogate_pair_end(charCode) {
+  return charCode >= 0xDC00 && charCode <= 0xDFFF;
+}
 
-module.exports = diff;
+function starts_with_pair_end(str) {
+  return is_surrogate_pair_end(str.charCodeAt(0));
+}
 
-/*
- * Modify a diff such that the cursor position points to the start of a change:
- * E.g.
- *   cursor_normalize_diff([[DIFF_EQUAL, 'abc']], 1)
- *     => [1, [[DIFF_EQUAL, 'a'], [DIFF_EQUAL, 'bc']]]
- *   cursor_normalize_diff([[DIFF_INSERT, 'new'], [DIFF_DELETE, 'xyz']], 2)
- *     => [2, [[DIFF_INSERT, 'new'], [DIFF_DELETE, 'xy'], [DIFF_DELETE, 'z']]]
- *
- * @param {Array} diffs Array of diff tuples
- * @param {Int} cursor_pos Suggested edit position. Must not be out of bounds!
- * @return {Array} A tuple [cursor location in the modified diff, modified diff]
- */
-function cursor_normalize_diff (diffs, cursor_pos) {
-  if (cursor_pos === 0) {
-    return [DIFF_EQUAL, diffs];
-  }
-  for (var current_pos = 0, i = 0; i < diffs.length; i++) {
-    var d = diffs[i];
-    if (d[0] === DIFF_DELETE || d[0] === DIFF_EQUAL) {
-      var next_pos = current_pos + d[1].length;
-      if (cursor_pos === next_pos) {
-        return [i + 1, diffs];
-      } else if (cursor_pos < next_pos) {
-        // copy to prevent side effects
-        diffs = diffs.slice();
-        // split d into two diff changes
-        var split_pos = cursor_pos - current_pos;
-        var d_left = [d[0], d[1].slice(0, split_pos)];
-        var d_right = [d[0], d[1].slice(split_pos)];
-        diffs.splice(i, 1, d_left, d_right);
-        return [i + 1, diffs];
-      } else {
-        current_pos = next_pos;
-      }
-    }
-  }
-  throw new Error('cursor_pos is out of bounds!')
+function ends_with_pair_start(str) {
+  return is_surrogate_pair_start(str.charCodeAt(str.length - 1));
 }
 
-/*
- * Modify a diff such that the edit position is "shifted" to the proposed edit location (cursor_position).
- *
- * Case 1)
- *   Check if a naive shift is possible:
- *     [0, X], [ 1, Y] -> [ 1, Y], [0, X]    (if X + Y === Y + X)
- *     [0, X], [-1, Y] -> [-1, Y], [0, X]    (if X + Y === Y + X) - holds same result
- * Case 2)
- *   Check if the following shifts are possible:
- *     [0, 'pre'], [ 1, 'prefix'] -> [ 1, 'pre'], [0, 'pre'], [ 1, 'fix']
- *     [0, 'pre'], [-1, 'prefix'] -> [-1, 'pre'], [0, 'pre'], [-1, 'fix']
- *         ^            ^
- *         d          d_next
- *
- * @param {Array} diffs Array of diff tuples
- * @param {Int} cursor_pos Suggested edit position. Must not be out of bounds!
- * @return {Array} Array of diff tuples
- */
-function fix_cursor (diffs, cursor_pos) {
-  var norm = cursor_normalize_diff(diffs, cursor_pos);
-  var ndiffs = norm[1];
-  var cursor_pointer = norm[0];
-  var d = ndiffs[cursor_pointer];
-  var d_next = ndiffs[cursor_pointer + 1];
-
-  if (d == null) {
-    // Text was deleted from end of original string,
-    // cursor is now out of bounds in new string
-    return diffs;
-  } else if (d[0] !== DIFF_EQUAL) {
-    // A modification happened at the cursor location.
-    // This is the expected outcome, so we can return the original diff.
-    return diffs;
-  } else {
-    if (d_next != null && d[1] + d_next[1] === d_next[1] + d[1]) {
-      // Case 1)
-      // It is possible to perform a naive shift
-      ndiffs.splice(cursor_pointer, 2, d_next, d)
-      return merge_tuples(ndiffs, cursor_pointer, 2)
-    } else if (d_next != null && d_next[1].indexOf(d[1]) === 0) {
-      // Case 2)
-      // d[1] is a prefix of d_next[1]
-      // We can assume that d_next[0] !== 0, since d[0] === 0
-      // Shift edit locations..
-      ndiffs.splice(cursor_pointer, 2, [d_next[0], d[1]], [0, d[1]]);
-      var suffix = d_next[1].slice(d[1].length);
-      if (suffix.length > 0) {
-        ndiffs.splice(cursor_pointer + 2, 0, [d_next[0], suffix]);
-      }
-      return merge_tuples(ndiffs, cursor_pointer, 3)
-    } else {
-      // Not possible to perform any modification
-      return diffs;
+function remove_empty_tuples(tuples) {
+  var ret = [];
+  for (var i = 0; i < tuples.length; i++) {
+    if (tuples[i][1].length > 0) {
+      ret.push(tuples[i]);
     }
   }
+  return ret;
 }
 
-/*
- * Check diff did not split surrogate pairs.
- * Ex. [0, '\uD83D'], [-1, '\uDC36'], [1, '\uDC2F'] -> [-1, '\uD83D\uDC36'], [1, '\uD83D\uDC2F']
- *     '\uD83D\uDC36' === '🐶', '\uD83D\uDC2F' === '🐯'
- *
- * @param {Array} diffs Array of diff tuples
- * @return {Array} Array of diff tuples
- */
-function fix_emoji (diffs) {
-  var compact = false;
-  var starts_with_pair_end = function(str) {
-    return str.charCodeAt(0) >= 0xDC00 && str.charCodeAt(0) <= 0xDFFF;
+function make_edit_splice(before, oldMiddle, newMiddle, after) {
+  if (ends_with_pair_start(before) || starts_with_pair_end(after)) {
+    return null;
   }
-  var ends_with_pair_start = function(str) {
-    return str.charCodeAt(str.length-1) >= 0xD800 && str.charCodeAt(str.length-1) <= 0xDBFF;
-  }
-  for (var i = 2; i < diffs.length; i += 1) {
-    if (diffs[i-2][0] === DIFF_EQUAL && ends_with_pair_start(diffs[i-2][1]) &&
-        diffs[i-1][0] === DIFF_DELETE && starts_with_pair_end(diffs[i-1][1]) &&
-        diffs[i][0] === DIFF_INSERT && starts_with_pair_end(diffs[i][1])) {
-      compact = true;
+  return remove_empty_tuples([
+    [DIFF_EQUAL, before],
+    [DIFF_DELETE, oldMiddle],
+    [DIFF_INSERT, newMiddle],
+    [DIFF_EQUAL, after]
+  ]);
+}
 
-      diffs[i-1][1] = diffs[i-2][1].slice(-1) + diffs[i-1][1];
-      diffs[i][1] = diffs[i-2][1].slice(-1) + diffs[i][1];
-
-      diffs[i-2][1] = diffs[i-2][1].slice(0, -1);
+function find_cursor_edit_diff(oldText, newText, cursor_pos) {
+  // note: this runs after equality check has ruled out exact equality
+  var oldRange = typeof cursor_pos === 'number' ?
+    { index: cursor_pos, length: 0 } : cursor_pos.oldRange;
+  var newRange = typeof cursor_pos === 'number' ?
+    null : cursor_pos.newRange;
+  // take into account the old and new selection to generate the best diff
+  // possible for a text edit.  for example, a text change from "xxx" to "xx"
+  // could be a delete or forwards-delete of any one of the x's, or the
+  // result of selecting two of the x's and typing "x".
+  var oldLength = oldText.length;
+  var newLength = newText.length;
+  if (oldRange.length === 0 && (newRange === null || newRange.length === 0)) {
+    // see if we have an insert or delete before or after cursor
+    var oldCursor = oldRange.index;
+    var oldBefore = oldText.slice(0, oldCursor);
+    var oldAfter = oldText.slice(oldCursor);
+    var maybeNewCursor = newRange ? newRange.index : null;
+    editBefore: {
+      // is this an insert or delete right before oldCursor?
+      var newCursor = oldCursor + newLength - oldLength;
+      if (maybeNewCursor !== null && maybeNewCursor !== newCursor) {
+        break editBefore;
+      }
+      if (newCursor < 0 || newCursor > newLength) {
+        break editBefore;
+      }
+      var newBefore = newText.slice(0, newCursor);
+      var newAfter = newText.slice(newCursor);
+      if (newAfter !== oldAfter) {
+        break editBefore;
+      }
+      var prefixLength = Math.min(oldCursor, newCursor);
+      var oldPrefix = oldBefore.slice(0, prefixLength);
+      var newPrefix = newBefore.slice(0, prefixLength);
+      if (oldPrefix !== newPrefix) {
+        break editBefore;
+      }
+      var oldMiddle = oldBefore.slice(prefixLength);
+      var newMiddle = newBefore.slice(prefixLength);
+      return make_edit_splice(oldPrefix, oldMiddle, newMiddle, oldAfter);
     }
-  }
-  if (!compact) {
-    return diffs;
-  }
-  var fixed_diffs = [];
-  for (var i = 0; i < diffs.length; i += 1) {
-    if (diffs[i][1].length > 0) {
-      fixed_diffs.push(diffs[i]);
+    editAfter: {
+      // is this an insert or delete right after oldCursor?
+      if (maybeNewCursor !== null && maybeNewCursor !== oldCursor) {
+        break editAfter;
+      }
+      var cursor = oldCursor;
+      var newBefore = newText.slice(0, cursor);
+      var newAfter = newText.slice(cursor);
+      if (newBefore !== oldBefore) {
+        break editAfter;
+      }
+      var suffixLength = Math.min(oldLength - cursor, newLength - cursor);
+      var oldSuffix = oldAfter.slice(oldAfter.length - suffixLength);
+      var newSuffix = newAfter.slice(newAfter.length - suffixLength);
+      if (oldSuffix !== newSuffix) {
+        break editAfter;
+      }
+      var oldMiddle = oldAfter.slice(0, oldAfter.length - suffixLength);
+      var newMiddle = newAfter.slice(0, newAfter.length - suffixLength);
+      return make_edit_splice(oldBefore, oldMiddle, newMiddle, oldSuffix);
     }
   }
-  return fixed_diffs;
-}
-
-/*
- * Try to merge tuples with their neigbors in a given range.
- * E.g. [0, 'a'], [0, 'b'] -> [0, 'ab']
- *
- * @param {Array} diffs Array of diff tuples.
- * @param {Int} start Position of the first element to merge (diffs[start] is also merged with diffs[start - 1]).
- * @param {Int} length Number of consecutive elements to check.
- * @return {Array} Array of merged diff tuples.
- */
-function merge_tuples (diffs, start, length) {
-  // Check from (start-1) to (start+length).
-  for (var i = start + length - 1; i >= 0 && i >= start - 1; i--) {
-    if (i + 1 < diffs.length) {
-      var left_d = diffs[i];
-      var right_d = diffs[i+1];
-      if (left_d[0] === right_d[1]) {
-        diffs.splice(i, 2, [left_d[0], left_d[1] + right_d[1]]);
+  if (oldRange.length > 0 && newRange && newRange.length === 0) {
+    replaceRange: {
+      // see if diff could be a splice of the old selection range
+      var oldPrefix = oldText.slice(0, oldRange.index);
+      var oldSuffix = oldText.slice(oldRange.index + oldRange.length);
+      var prefixLength = oldPrefix.length;
+      var suffixLength = oldSuffix.length;
+      if (newLength < prefixLength + suffixLength) {
+        break replaceRange;
       }
+      var newPrefix = newText.slice(0, prefixLength);
+      var newSuffix = newText.slice(newLength - suffixLength);
+      if (oldPrefix !== newPrefix || oldSuffix !== newSuffix) {
+        break replaceRange;
+      }
+      var oldMiddle = oldText.slice(prefixLength, oldLength - suffixLength);
+      var newMiddle = newText.slice(prefixLength, newLength - suffixLength);
+      return make_edit_splice(oldPrefix, oldMiddle, newMiddle, oldSuffix);
     }
   }
-  return diffs;
+
+  return null;
 }
+
+function diff(text1, text2, cursor_pos) {
+  // only pass fix_unicode=true at the top level, not when diff_main is
+  // recursively invoked
+  return diff_main(text1, text2, cursor_pos, true);
+}
+
+diff.INSERT = DIFF_INSERT;
+diff.DELETE = DIFF_DELETE;
+diff.EQUAL = DIFF_EQUAL;
+
+module.exports = diff;

package.json

 {
   "name": "fast-diff",
-  "version": "1.1.2",
+  "version": "1.2.0",
   "description": "Fast Javascript text diff",
   "author": "Jason Chen <[e-mail]>",
   "main": "diff.js",
+  "types": "diff.d.ts",
   "devDependencies": {
-    "googlediff": "~0.1.0",
     "lodash": "~3.9.3",
@@ -23,3 +23,5 @@ "seedrandom": "~2.4.0"
   "license": "Apache-2.0",
-  "keywords": ["diff"]
+  "keywords": [
+    "diff"
+  ]
 }

test.js

 var _ = require('lodash');
-var googlediff = require('googlediff');
 var seedrandom = require('seedrandom');
 var diff = require('./diff.js');
 
-googlediff = new googlediff();
-
 var ITERATIONS = 10000;
 var ALPHABET = 'GATTACA';
 var LENGTH = 100;
+var EMOJI_MAX_LENGTH = 50;
 
@@ -15,2 +13,17 @@ var seed = Math.floor(Math.random() * 10000);
 
+console.log('Running regression tests...');
+[
+  ['GAATAAAAAAAGATTAACAT', 'AAAAACTTGTAATTAACAAC'],
+  ['🔘🤘🔗🔗', '🔗🤗🤗__🤗🤘🤘🤗🔗🤘🔗'],
+  ['🔗🤗🤗__🤗🤘🤘🤗🔗🤘🔗', '🤗🤘🔘'],
+  ['🤘🤘🔘🔘_🔘🔗🤘🤗🤗__🔗🤘', '🤘🔘🤘🔗🤘🤘🔗🤗🤘🔘🔘'],
+  ['🤗🤘🤗🔘🤘🔘🤗_🤗🔗🤘🤗_🤘🔗🤗🤘🔗🤘🤘🤘🔗🤗🔗🔗🔗🤗_🤘🔗🤗🤗🔘🤗🤗🤘🤗',
+   '_🤗🤘_🤘🤘🔘🤗🔘🤘_🔘🤗🔗🔘🔗🤘🔗🤘🤗🔗🔗🔗🤘🔘_🤗🤘🤘🤘__🤘_🔘🤘🤘_🔗🤘🔘'],
+  ['🔗🤘🤗🔘🔘🤗', '🤘🤘🤘🤗🔘🔗🔗'],
+  ['🔘_🔗🔗🔗🤗🔗', '🤘🤗🔗🤗_🤘🔘_'],
+].forEach(function (data) {
+  var result = diff(data[0], data[1]);
+  applyDiff(result, data[0], data[1]);
+});
+
 console.log('Running computing ' + ITERATIONS + ' diffs with seed ' + seed + '...');
@@ -20,5 +33,5 @@
 var strings = [];
-for(var i = 0; i <= ITERATIONS; ++i) {
+for (var i = 0; i <= ITERATIONS; ++i) {
   var chars = [];
-  for(var l = 0; l < LENGTH; ++l) {
+  for (var l = 0; l < LENGTH; ++l) {
     var letter = ALPHABET.substr(Math.floor(random() * ALPHABET.length), 1);
@@ -30,65 +43,295 @@ chars.push(letter);
 
-console.log('Running tests *without* cursor information...');
-for(var i = 0; i < ITERATIONS; ++i) {
-  var result = diff(strings[i], strings[i+1]);
-  var expected = googlediff.diff_main(strings[i], strings[i+1]);
-  if (!_.isEqual(result, expected)) {
-    console.log('Expected', expected);
-    console.log('Result', result);
-    throw new Error('Diff produced difference results.');
-  }
+console.log('Running fuzz tests *without* cursor information...');
+for (var i = 0; i < ITERATIONS; ++i) {
+  var result = diff(strings[i], strings[i + 1]);
+  applyDiff(result, strings[i], strings[i + 1]);
 }
 
-console.log('Running tests *with* cursor information');
-for(var i = 0; i < ITERATIONS; ++i) {
+console.log('Running fuzz tests *with* cursor information');
+for (var i = 0; i < ITERATIONS; ++i) {
   var cursor_pos = Math.floor(random() * strings[i].length + 1);
-  var diffs = diff(strings[i], strings[i+1], cursor_pos);
-  var patch = googlediff.patch_make(strings[i], strings[i+1], diffs);
-  var expected = googlediff.patch_apply(patch, strings[i])[0];
-  if (expected !== strings[i+1]) {
-    console.log('Expected', expected);
-    console.log('Result', strings[i+1]);
-    throw new Error('Diff produced difference results.');
+  var diffs = diff(strings[i], strings[i + 1], cursor_pos);
+  applyDiff(diffs, strings[i], strings[i + 1]);
+}
+
+function parseDiff(str) {
+  if (!str) {
+    return [];
   }
+  return str.split(/(?=[+\-=])/).map(function (piece) {
+    var symbol = piece.charAt(0);
+    var text = piece.slice(1);
+    return [
+      symbol === '+' ? diff.INSERT : symbol === '-' ? diff.DELETE : diff.EQUAL,
+      text
+    ]
+  });
 }
 
-console.log('Running emoji tests');
-(function() {
-  var result = diff('🐶', '🐯');
-  var expected = [
-    [diff.DELETE, '🐶'],
-    [diff.INSERT, '🐯'],
-  ];
-  if (!_.isEqual(result, expected)) {
-    console.log(result, '!==', expected);
-    throw new Error('Emoji simple case test failed');
+console.log('Running cursor tests');
+[
+  ['', 0, '', null, ''],
+
+  ['', 0, 'a', null, '+a'],
+  ['a', 0, 'aa', null, '+a=a'],
+  ['a', 1, 'aa', null, '=a+a'],
+  ['aa', 0, 'aaa', null, '+a=aa'],
+  ['aa', 1, 'aaa', null, '=a+a=a'],
+  ['aa', 2, 'aaa', null, '=aa+a'],
+  ['aaa', 0, 'aaaa', null, '+a=aaa'],
+  ['aaa', 1, 'aaaa', null, '=a+a=aa'],
+  ['aaa', 2, 'aaaa', null, '=aa+a=a'],
+  ['aaa', 3, 'aaaa', null, '=aaa+a'],
+
+  ['a', 0, '', null, '-a'],
+  ['a', 1, '', null, '-a'],
+  ['aa', 0, 'a', null, '-a=a'],
+  ['aa', 1, 'a', null, '-a=a'],
+  ['aa', 2, 'a', null, '=a-a'],
+  ['aaa', 0, 'aa', null, '-a=aa'],
+  ['aaa', 1, 'aa', null, '-a=aa'],
+  ['aaa', 2, 'aa', null, '=a-a=a'],
+  ['aaa', 3, 'aa', null, '=aa-a'],
+
+  ['', 0, '', 0, ''],
+
+  ['', 0, 'a', 1, '+a'],
+  ['a', 0, 'aa', 1, '+a=a'],
+  ['a', 1, 'aa', 2, '=a+a'],
+  ['aa', 0, 'aaa', 1, '+a=aa'],
+  ['aa', 1, 'aaa', 2, '=a+a=a'],
+  ['aa', 2, 'aaa', 3, '=aa+a'],
+  ['aaa', 0, 'aaaa', 1, '+a=aaa'],
+  ['aaa', 1, 'aaaa', 2, '=a+a=aa'],
+  ['aaa', 2, 'aaaa', 3, '=aa+a=a'],
+  ['aaa', 3, 'aaaa', 4, '=aaa+a'],
+
+  ['a', 1, '', 0, '-a'],
+  ['aa', 1, 'a', 0, '-a=a'],
+  ['aa', 2, 'a', 1, '=a-a'],
+  ['aaa', 1, 'aa', 0, '-a=aa'],
+  ['aaa', 2, 'aa', 1, '=a-a=a'],
+  ['aaa', 3, 'aa', 2, '=aa-a'],
+
+  ['a', 1, '', 0, '-a'],
+  ['aa', 1, 'a', 0, '-a=a'],
+  ['aa', 2, 'a', 1, '=a-a'],
+  ['aaa', 1, 'aa', 0, '-a=aa'],
+  ['aaa', 2, 'aa', 1, '=a-a=a'],
+  ['aaa', 3, 'aa', 2, '=aa-a'],
+
+  // forward-delete
+  ['a', 0, '', 0, '-a'],
+  ['aa', 0, 'a', 0, '-a=a'],
+  ['aa', 1, 'a', 1, '=a-a'],
+  ['aaa', 0, 'aa', 0, '-a=aa'],
+  ['aaa', 1, 'aa', 1, '=a-a=a'],
+  ['aaa', 2, 'aa', 2, '=aa-a'],
+
+  ['bob', 0, 'bobob', null, '+bo=bob'],
+  ['bob', 1, 'bobob', null, '=b+ob=ob'],
+  ['bob', 2, 'bobob', null, '=bo+bo=b'],
+  ['bob', 3, 'bobob', null, '=bob+ob'],
+  ['bob', 0, 'bobob', 2, '+bo=bob'],
+  ['bob', 1, 'bobob', 3, '=b+ob=ob'],
+  ['bob', 2, 'bobob', 4, '=bo+bo=b'],
+  ['bob', 3, 'bobob', 5, '=bob+ob'],
+  ['bobob', 2, 'bob', null, '-bo=bob'],
+  ['bobob', 3, 'bob', null, '=b-ob=ob'],
+  ['bobob', 4, 'bob', null, '=bo-bo=b'],
+  ['bobob', 5, 'bob', null, '=bob-ob'],
+  ['bobob', 2, 'bob', 0, '-bo=bob'],
+  ['bobob', 3, 'bob', 1, '=b-ob=ob'],
+  ['bobob', 4, 'bob', 2, '=bo-bo=b'],
+  ['bobob', 5, 'bob', 3, '=bob-ob'],
+
+  ['bob', 1, 'b', null, '=b-ob'],
+
+  ['hello', [0, 5], 'h', 1, '-hello+h'],
+  ['yay', [0, 3], 'y', 1, '-yay+y'],
+  ['bobob', [1, 4], 'bob', 2, '=b-obo+o=b'],
+
+].forEach(function (data) {
+  var oldText = data[0];
+  var newText = data[2];
+  var oldRange = typeof data[1] === 'number' ?
+    { index: data[1], length: 0 } :
+    { index: data[1][0], length: data[1][1] - data[1][0] };
+  var newRange = typeof data[3] === 'number' ?
+    { index: data[3], length: 0 } :
+    data[3] === null ? null : { index: data[3][0], length: data[3][1] - data[3][0] };
+  var expected = parseDiff(data[4]);
+  if (newRange === null && typeof data[1] !== 'number') {
+    throw new Error('invalid test case');
   }
-})();
+  var cursorInfo = newRange === null ? data[1] : {
+    oldRange: oldRange,
+    newRange: newRange,
+  };
+  doCursorTest(oldText, newText, cursorInfo, expected);
+  doCursorTest('x' + oldText, 'x' + newText, shiftCursorInfo(cursorInfo, 1), diffPrepend(expected, 'x'));
+  doCursorTest(oldText + 'x', newText + 'x', cursorInfo, diffAppend(expected, 'x'));
+});
 
-(function() {
-  var result = diff('👨🏽', '👩🏽');
-  var expected = [
-    [diff.DELETE, '👨'],
-    [diff.INSERT, '👩'],
-    [diff.EQUAL, '🏽']
-  ];
+function diffPrepend(tuples, text) {
+  if (tuples.length > 0 && tuples[0][0] === diff.EQUAL) {
+    return [[diff.EQUAL, text + tuples[0][1]]].concat(tuples.slice(1));
+  } else {
+    return [[diff.EQUAL, text]].concat(tuples);
+  }
+}
+
+function diffAppend(tuples, text) {
+  var lastTuple = tuples[tuples.length - 1];
+  if (lastTuple && lastTuple[0] === diff.EQUAL) {
+    return tuples.slice(0, -1).concat([[diff.EQUAL, lastTuple[1] + text]]);
+  } else {
+    return tuples.concat([[diff.EQUAL, text]]);
+  }
+}
+
+function shiftCursorInfo(cursorInfo, amount) {
+  if (typeof cursorInfo === 'number') {
+    return cursorInfo + amount;
+  } else {
+    return {
+      oldRange: {
+        index: cursorInfo.oldRange.index + amount,
+        length: cursorInfo.oldRange.length,
+      },
+      newRange: {
+        index: cursorInfo.newRange.index + amount,
+        length: cursorInfo.newRange.length,
+      },
+    }
+  }
+}
+
+function doCursorTest(oldText, newText, cursorInfo, expected) {
+  var result = diff(oldText, newText, cursorInfo);
   if (!_.isEqual(result, expected)) {
+    console.log([oldText, newText, cursorInfo]);
     console.log(result, '!==', expected);
-    throw new Error('Emoji before case test failed');
+    throw new Error('cursor test failed');
   }
-})();
+}
 
-(function() {
-  var result = diff('👩🏼', '👩🏽');
-  var expected = [
-    [diff.EQUAL, '👩'],
-    [diff.DELETE, '🏼'],
-    [diff.INSERT, '🏽'],
-  ];
+console.log('Running emoji tests');
+[
+  ['🐶', '🐯', '-🐶+🐯'],
+  ['👨🏽', '👩🏽', '-👨+👩=🏽'],
+  ['👩🏼', '👩🏽', '=👩-🏼+🏽'],
+
+  ['🍏🍎', '🍎', '-🍏=🍎'],
+  ['🍎', '🍏🍎', '+🍏=🍎'],
+
+].forEach(function (data) {
+  var oldText = data[0];
+  var newText = data[1];
+  var expected = parseDiff(data[2]);
+  doEmojiTest(oldText, newText, expected);
+  doEmojiTest('x' + oldText, 'x' + newText, diffPrepend(expected, 'x'));
+  doEmojiTest(oldText + 'x', newText + 'x', diffAppend(expected, 'x'));
+});
+
+function doEmojiTest(oldText, newText, expected) {
+  var result = diff(oldText, newText);
   if (!_.isEqual(result, expected)) {
+    console.log(oldText, newText, expected);
     console.log(result, '!==', expected);
-    throw new Error('Emoji after case test failed');
+    throw new Error('Emoji simple test case failed');
   }
-})();
+}
 
+// emojis chosen to share high and low surrogates!
+var EMOJI_ALPHABET = ['_', '🤗', '🔗', '🤘', '🔘'];
+
+console.log('Generating emoji strings...');
+var emoji_strings = [];
+for (var i = 0; i <= ITERATIONS; ++i) {
+  var letters = [];
+  var len = Math.floor(random() * EMOJI_MAX_LENGTH);
+  for (var l = 0; l < len; ++l) {
+    var letter = EMOJI_ALPHABET[Math.floor(random() * EMOJI_ALPHABET.length)];
+    letters.push(letter);
+  }
+  emoji_strings.push(letters.join(''));
+}
+
+console.log('Running emoji fuzz tests...');
+for (var i = 0; i < ITERATIONS; ++i) {
+  var oldText = emoji_strings[i];
+  var newText = emoji_strings[i + 1];
+  var result = diff(oldText, newText);
+  applyDiff(result, oldText, newText);
+}
+
+// Applies a diff to text, throwing an error if diff is invalid or incorrect
+function applyDiff(diffs, text, expectedResult) {
+  var pos = 0;
+  function throwError(message) {
+    console.log(diffs, text, expectedResult);
+    throw new Error(message);
+  }
+  function expect(expected) {
+    var found = text.substr(pos, expected.length);
+    if (found !== expected) {
+      throwError('Expected "' + expected + '", found "' + found + '"');
+    }
+  }
+  var result = '';
+  var inserts_since_last_equality = 0;
+  var deletes_since_last_equality = 0;
+  for (var i = 0; i < diffs.length; i++) {
+    var d = diffs[i];
+    if (!d[1]) {
+      throwError('Empty tuple in diff')
+    }
+    var firstCharCode = d[1].charCodeAt(0);
+    var lastCharCode = d[1].slice(-1).charCodeAt(0);
+    if (firstCharCode >= 0xDC00 && firstCharCode <= 0xDFFF ||
+      lastCharCode >= 0xD800 && lastCharCode <= 0xDBFF) {
+        throwError('Bad unicode diff tuple')
+    }
+    switch (d[0]) {
+      case diff.EQUAL:
+        if (i !== 0 && !inserts_since_last_equality && !deletes_since_last_equality) {
+          throwError('two consecutive equalities in diff');
+        }
+        inserts_since_last_equality = 0;
+        deletes_since_last_equality = 0;
+        expect(d[1]);
+        result += d[1];
+        pos += d[1].length;
+        break;
+      case diff.DELETE:
+        if (deletes_since_last_equality) {
+          throwError('multiple deletes between equalities')
+        }
+        if (inserts_since_last_equality) {
+          throwError('delete following insert in diff')
+        }
+        deletes_since_last_equality++;
+        expect(d[1]);
+        pos += d[1].length;
+        break
+      case diff.INSERT:
+        if (inserts_since_last_equality) {
+          throwError('multiple inserts between equalities')
+        }
+        inserts_since_last_equality++;
+        result += d[1];
+        break;
+    }
+  }
+  if (pos !== text.length) {
+    throwError('Diff did not consume entire input text');
+  }
+  if (result !== expectedResult) {
+    console.log(diffs, text, expectedResult, result);
+    throw new Error('Diff not correct')
+  }
+  return result;
+}
+
 console.log("Success!");

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increased by33.32%

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