Merge pull request #652 from yazeedb/add-when

Add when()

snippets/when.md

@@ -0,0 +1,18 @@
+### when
+
+Tests a value, `x`, against a predicate function. If `true`, return `fn(x)`. Else, return `x`. 
+
+Return a function expecting a single value, `x`, that returns the appropriate value based on `pred`.
+
+```js
+const when = (pred, whenTrue) => (x) => pred(x) ? whenTrue(x) : x;
+```
+
+```js
+const doubleEvenNumbers = when(
+  (x) => x % 2 === 0,
+  (x) => x * 2
+);
+doubleEvenNumbers(2); // 4
+doubleEvenNumbers(1); // 1
+```

tag_database

@@ -291,6 +291,7 @@ URLJoin:string,utility,regexp
 UUIDGeneratorBrowser:browser,utility,random
 UUIDGeneratorNode:node,utility,random
 validateNumber:utility,math
+when:function
 without:array
 words:string,regexp
 xProd:array,math

test/when/when.js

@@ -0,0 +1,2 @@
+const when = (pred, whenTrue) => (x) => pred(x) ? whenTrue(x) : x;
+module.exports = when;

test/when/when.test.js

@@ -0,0 +1,18 @@
+const test = require('tape');
+const when = require('./when.js');
+
+test('Testing when', (t) => {
+  //For more information on all the methods supported by tape
+  //Please go to https://github.com/substack/tape
+  t.true(typeof when === 'function', 'when is a Function');
+
+  const doubleEvenNumbers = when(
+    (x) => x % 2 === 0,
+    (x) => x * 2
+  );
+
+  t.true(doubleEvenNumbers(2) === 4);
+  t.true(doubleEvenNumbers(1) === 1);
+
+  t.end();
+});