lazy-ass - npm Package Compare versions

Comparing version 0.2.0 to 0.4.0

bower.json

 {
   "name": "lazy-ass",
   "main": "index.js",
-  "version": "0.2.0",
+  "version": "0.4.0",
   "homepage": "https://github.com/bahmutov/lazy-ass",
@@ -6,0 +6,0 @@ "license": "MIT",

index.js

@@ -17,2 +17,5 @@ (function initLazyAss() {
       }
+      if (arg instanceof Error) {
+        return total + arg.name + ' ' + arg.message;
+      }
       return total + JSON.stringify(arg, null, 2);
@@ -23,14 +26,29 @@ }, '');
 
-  var lazyAss = function lazyAss(condition) {
+  function lazyAssLogic(condition) {
+    var fn = typeof condition === 'function' ? condition : null;
+
+    if (fn) {
+      condition = fn();
+    }
     if (!condition) {
       var args = [].slice.call(arguments, 1);
-      throw new Error(formMessage(args));
+      if (fn) {
+        args.unshift(fn.toString());
+      }
+      return new Error(formMessage(args));
     }
+  }
+
+  var lazyAss = function lazyAss() {
+    var err = lazyAssLogic.apply(null, arguments);
+    if (err) {
+      throw err;
+    }
   };
 
-  var lazyAssync = function lazyAssync(condition) {
-    if (!condition) {
-      var args = [].slice.call(arguments, 1);
+  var lazyAssync = function lazyAssync() {
+    var err = lazyAssLogic.apply(null, arguments);
+    if (err) {
       setTimeout(function () {
-        throw new Error(formMessage(args));
+        throw err;
       }, 0);
@@ -37,0 +55,0 @@ }

package.json

 {
   "name": "lazy-ass",
   "description": "Lazy assertions without performance penalty",
-  "version": "0.2.0",
+  "version": "0.4.0",
   "author": "Gleb Bahmutov <[e-mail]>",
@@ -6,0 +6,0 @@ "bugs": {

README.md

@@ -29,2 +29,15 @@ # lazy-ass
 
+Concatenates strings, stringifies objects, calls functions - only if
+condition is false.
+
+```js
+function environment() {
+  // returns string
+}
+var user = {} // an object
+lazyAsync(condition, 'something went wrong for', user, 'in', environment);
+// throws an error with message equivalent of
+// 'something went wrong for ' + JSON.stringify(user) + ' in ' + environment()
+```
+
 ## Why?
@@ -86,2 +99,44 @@
 
+## Predicate function as a condition
+
+Typically, JavaScript evaluates the condition expression first, then calls *lazyAss*.
+This means the function itself sees only the true / false result, and not the expression
+itself. This makes makes the error messages cryptic
+
+    lazyAss(2 + 2 === 5);
+    // Error
+
+We usually get around this by giving at least one additional message argument to
+explain the condition tested
+
+    lazyAss(2 + 2 === 5, 'addition')
+    // Error: addition
+
+*lazyAss* has a better solution: if you give a function that evaluates the condition
+expression, if the function returns false, the error message will include the source
+of the function, making the extra arguments unnecessary
+
+    lazyAss(function () { return 2 + 2 === 5; });
+    // Error: function () { return 2 + 2 === 5; }
+
+The condition function has access to any variables in the scope, making it extremely
+powerful
+
+    var foo = 2, bar = 2;
+    lazyAss(function () { return foo + bar === 5; });
+    // Error: function () { return foo + bar === 5; }
+
+In practical terms, I recommend using separate predicates function and
+passing relevant values to the *lazyAss* function. Remember, there is no performance
+penalty!
+
+    var foo = 2, bar = 2;
+    function isValidPair() {
+      return foo + bar === 5;
+    }
+    lazyAss(isValidPair, 'foo', foo, 'bar', bar);
+    // Error: function isValidPair() {
+    //   return foo + bar === 5;
+    // } foo 2 bar 2
+
 ### Small print
@@ -88,0 +143,0 @@

test/lazy-ass.spec.js

@@ -80,3 +80,67 @@ /* global lazyAss */
     });
+
+    it('takes error name and message', function () {
+      expect(function () {
+        lazyAss(false, new Error('hi there'));
+      }).to.throwException(function (err) {
+        expect(err.message).to.contain('Error');
+        expect(err.message).to.contain('hi there');
+      });
+    });
   });
+
+  describe('function as condition', function () {
+    it('evaluates the function', function () {
+      var called;
+      function condition() { called = true; return true; }
+
+      lazyAss(condition);
+      expect(called).to.be(true);
+    });
+
+    it('no result is failure', function () {
+      function noreturn() {}
+
+      expect(function () {
+        lazyAss(noreturn);
+      }).to.throwError();
+    });
+
+    it('adds condition function source to message', function () {
+      function myCondition() {}
+      expect(function () {
+        lazyAss(myCondition);
+      }).to.throwException(/myCondition/);
+    });
+
+    it('allows anonymous functions', function () {
+      var called;
+      lazyAss(function() { return true; });
+      lazyAss(function() { return true; }, 'everything is ok');
+      lazyAss(function() { called = true; return true; }, 'everything is ok');
+      expect(called).to.be(true);
+
+      expect(function () {
+        lazyAss(function () {});
+      }).to.throwError();
+    });
+
+    it('has access via closure', function () {
+      var foo = 2, bar = 3;
+      expect(function () {
+        lazyAss(function () { return foo + bar === 6; }, 'addition');
+      }).to.throwException(function (err) {
+        expect(err.message).to.contain('foo + bar');
+        expect(err.message).to.contain('addition');
+      });
+    });
+
+    it('example', function () {
+      var foo = 2, bar = 2;
+      function isValidPair() {
+        return foo + bar === 4;
+      }
+      lazyAss(isValidPair, 'foo', foo, 'bar', bar);
+    });
+  });
 });

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Improved metrics

Total package byte prevSize

21870

increased by22.35%

Lines of code

367

increased by23.57%

Number of lines in readme file

190

increased by40.74%

No dependency changes