String#padStart and String#padEnd

README.md

@@ -440,6 +440,13 @@ You can use `$` and `#` for defining parameters.
 
 Aliases: `String#tpl()` & `String#template()`
 
+#### padStart / padEnd
+
+```js
+'foo'.padStart(10, 'bar') // barbarbfoo
+'foo'.padEnd(10, 'bar') // foobarbarb
+```
+
 #### repeat
 
 [http://people.mozilla.org/\~jorendorff/es6-draft.html#sec-string.prototype.repeat](http://people.mozilla.org/~jorendorff/es6-draft.html#sec-string.prototype.repeat)

lib/string.js

@@ -213,3 +213,13 @@ if (isUndefined(proto.repeat)) {
 if (isUndefined(String.isString)) {
   String.isString = isString
 }
+
+var padding = require('./string/padding')
+
+if (isUndefined(proto.padStart)) {
+  proto.padStart = padding.padStart
+}
+
+if (isUndefined(proto.padEnd)) {
+  proto.padEnd = padding.padEnd
+}

lib/string/padding.js

@@ -0,0 +1,53 @@
+var proto = String.prototype
+var bind = require('../var/defineFn')(proto)
+var repeat = require('./repeat')
+var isString = require('../var/isString')
+var isUndefined = require('../var/isUndefined')
+
+function getPadString (padString) {
+  if (isUndefined(padString)) {
+    return ' '
+  }
+
+  if (!isString(padString)) {
+    return String(padString)
+  }
+
+  return padString
+}
+
+function repeatPadString (str, padString, targetlength) {
+  var len = targetlength - str.length
+
+  if (len <= 0) {
+    return ''
+  }
+
+  if (len === padString.length) {
+    return padString
+  }
+
+  if (len > padString.length) {
+    padString = repeat(padString, Math.ceil(len / padString.length)).slice(0, len)
+  }
+
+  return padString.slice(0, len)
+}
+
+module.exports = {
+  padStart: function padStart (targetlength, padString) {
+    var ps = getPadString(padString)
+
+    var str = this
+
+    return ps ? repeatPadString(str, ps, targetlength) + str : str
+  },
+
+  padEnd: function padEnd (targetlength, padString) {
+    var ps = getPadString(padString)
+
+    var str = this
+
+    return ps ? str + repeatPadString(str, ps, targetlength) : str
+  }
+}

test/string.js

@@ -169,4 +169,36 @@ describe('String', function () {
       assert.equal(false, 'foo'.caseCmp('Foo', true))
     })
   })
+
+  describe('#padStart()', function () {
+    it('should pads string with a given string', function () {
+      var str = 'foo'
+
+      assert.equal(str.padStart(10), '       foo')
+      assert.equal(str.padStart(10, undefined), '       foo')
+      assert.equal(str.padStart(10, null), 'nullnulfoo')
+      assert.equal(str.padStart(10, true), 'truetrufoo')
+      assert.equal(str.padStart(10, 1), '1111111foo')
+      assert.equal(str.padStart(10, 'bar'), 'barbarbfoo')
+      assert.equal(str.padStart(10, {}), '[objectfoo')
+      assert.equal(str.padStart(10, []), 'foo')
+      assert.equal(str.padStart(10, /\s/), '/\\s//\\sfoo')
+    })
+  })
+
+  describe('#padEnd()', function () {
+    it('should pads string with a given string', function () {
+      var str = 'foo'
+
+      assert.equal(str.padEnd(10), 'foo       ')
+      assert.equal(str.padEnd(10, undefined), 'foo       ')
+      assert.equal(str.padEnd(10, null), 'foonullnul')
+      assert.equal(str.padEnd(10, true), 'footruetru')
+      assert.equal(str.padEnd(10, 1), 'foo1111111')
+      assert.equal(str.padEnd(10, 'bar'), 'foobarbarb')
+      assert.equal(str.padEnd(10, {}), 'foo[object')
+      assert.equal(str.padEnd(10, []), 'foo')
+      assert.equal(str.padEnd(10, /\s/), 'foo/\\s//\\s')
+    })
+  })
 })