es6.string.starts-with.js 784 Bytes
// 21.1.3.18 String.prototype.startsWith(searchString [, position ])
'use strict';
var $export     = require('./$.export')
  , toLength    = require('./$.to-length')
  , context     = require('./$.string-context')
  , STARTS_WITH = 'startsWith'
  , $startsWith = ''[STARTS_WITH];

$export($export.P + $export.F * require('./$.fails-is-regexp')(STARTS_WITH), 'String', {
  startsWith: function startsWith(searchString /*, position = 0 */){
    var that   = context(this, searchString, STARTS_WITH)
      , $$     = arguments
      , index  = toLength(Math.min($$.length > 1 ? $$[1] : undefined, that.length))
      , search = String(searchString);
    return $startsWith
      ? $startsWith.call(that, search, index)
      : that.slice(index, index + search.length) === search;
  }
});