@stamp/fp-constructor - npm Package Compare versions

Comparing version 0.1.10 to 0.2.0

__tests__/index.js

 var compose = require('@stamp/compose');
 var FpConstructor = require('..');
 
-describe('@stamp/fp-constructor', function() {
-  it('adds .constructor should be the stamp itself', function() {
+describe('@stamp/fp-constructor Stamp.of', function() {
+  it('should add .of static method referring to the stamp', function() {
     var Stamp = compose(FpConstructor);
 
-    expect(Stamp.constructor).toBe(Stamp);
+    expect(Stamp.of).toBe(Stamp);
   });
 
-  it('.constructor presence regardless of composition chain', function() {
-    var Stamp = compose({staticProperties: {constructor: 1}})
+  it('should refer to the correct stamp regardless of other stamps in the composition', function() {
+    var Stamp = compose({staticProperties: {of: 1}})
       .compose(
-        {staticProperties: {constructor: 2}},
+        {staticProperties: {of: 2}},
         FpConstructor,
-        {staticProperties: {constructor: 3}}
-      ).compose({staticProperties: {constructor: 4}});
+        {staticProperties: {of: 3}}
+      ).compose({staticProperties: {of: 4}});
 
+    expect(Stamp.of).toBe(Stamp);
+  });
+});
+
+describe('@stamp/fp-constructor instance.constructor', function() {
+  it('should add .constructor method to the stamp', function() {
+    var Stamp = compose(FpConstructor);
+    var instance = Stamp();
+
+    expect(instance.constructor).toBe(Stamp);
+  });
+
+  it('should not be an own prop on the instance', function() {
+    var Stamp = compose(FpConstructor);
+    var instance = Stamp();
+
+    expect(Object.getPrototypeOf(instance).constructor).toBe(Stamp);
+  });
+
+  it('should refer to the correct stamp regardless of other stamps in the composition', function() {
+    var Stamp = compose({methods: {constructor: 1}})
+      .compose(
+        {methods: {constructor: 2}},
+        FpConstructor,
+        {methods: {constructor: 3}}
+      ).compose({methods: {constructor: 4}});
+    var instance = Stamp();
+
+    expect(instance.constructor).toBe(Stamp);
+  });
+
+  it('should not break other methods', function() {
+    var foo = function foo () {};
+    var bar = function bar () {};
+    var Stamp = compose({methods: {foo: foo}})
+      .compose(
+        FpConstructor
+      ).compose({methods: {bar: bar}});
+    var instance = Stamp();
+
+    expect(instance.foo).toBe(foo);
+    expect(instance.bar).toBe(bar);
+  });
+});
+
+
+describe('@stamp/fp-constructor Stamp.constructor (deprecated)', function() {
+  it('should add .constructor static method referring to the stamp', function() {
+    var Stamp = compose(FpConstructor);
+
     expect(Stamp.constructor).toBe(Stamp);
   });
 });

index.js

@@ -5,4 +5,7 @@ var compose = require('@stamp/compose');
   composers: [function (opts) {
+    opts.stamp.of = opts.stamp;
     opts.stamp.constructor = opts.stamp;
+    opts.stamp.compose.methods = opts.stamp.compose.methods || {};
+    opts.stamp.compose.methods.constructor = opts.stamp;
   }]
 });

package.json

 {
   "name": "@stamp/fp-constructor",
-  "version": "0.1.10",
+  "version": "0.2.0",
   "description": "Adds the Stamp.constructor property referencing Stamp itself",
@@ -5,0 +5,0 @@ "main": "index.js",

README.md

 # @stamp/fp-constructor
 
-_Adds the Stamp.constructor property referencing Stamp itself_
+* _Adds the `Stamp.of` static property referencing Stamp itself_
+* _Adds the `instance.constructor` property referencing Stamp itself_
 
@@ -9,7 +10,38 @@ By composing the `@stamp/fp-constructor` into your stamp
 ```
-you get the static method `.constructor`:
+you get the static method `.of`:
 ```js
-MyStamp.constructor === MyStamp // true
+MyStamp.of === MyStamp; // true
 ```
 
+and the instance method, `.constructor`:
+```js
+instance = MyStamp(/* ...options */);
+instance.constructor === MyStamp; // true
+```
+
+## Motivation
+
+Frequently, it's desirable to instantiate a new instance of a given datatype inside a generic function. However, JavaScript lacks a built-in way to do that which is reliable. Classes throw errors if you leave off `new`, and arrow function factories will throw if you try to instantiate an instance with `new`, and there's no standard way to inject a value into the new datatype.
+
+The `Stamp.of()` is a standard way to create a new value of a given stamp where the calling conventions are unambiguous: It does not require `new`, and you inject the value by passing the necessary arguments directly into the `.of()` static method.
+
+Having the `.of()` method only solves half of the problem, though. You still need a way got get a handle on the stamp from an object instance. You can do that with the `instance.constructor()` method.
+
+Here's an example of what you can do with the combination. The following `empty()` utility will return an empty instance of whatever supporting datatype you pass in, including standard JavaScript arrays:
+
+```js
+const empty = ({ constructor } = {}) => constructor.of ?
+  constructor.of() :
+  undefined
+;
+
+const foo = [23];
+
+console.log(
+  empty(foo) // []
+);
+```
+
+All [applicative functors](https://github.com/fantasyland/fantasy-land#applicative) in JavaScript should implement `.of()`.
+
 ## Usage
@@ -28,2 +60,7 @@
 #### methods
-`stamp.constructor(...args) -> Object`
+`stamp.of(...args) => Object`
+
+### Instance methods
+
+### methods
+`instance.constructor(...args) => Object`

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Improved metrics

Total package byte prevSize

4881

increased by190.88%

Lines of code

65

increased by182.61%

Number of lines in readme file

65

increased by132.14%

Worsened metrics

Number of medium supply chain risk alerts

1

increased byInfinity%

No dependency changes