Question

I’ve recently been looking at functional programming with Javascript, to which I’m a noob.

While writing some ‘map’, ‘reduce’ and ‘find’ functions I discover that as of JS version 1.5 these functions are already available (see https://developer.mozilla.org/en/Core_JavaScript_1.5_Reference/Global_Objects/Array)

I am however confused as next to these functions (i.e reduce) it says ‘requires javscript 1.8’ – but its in the 1.5 docs? How can this be ?

Also does anyone have a list, of all the major browsers, against which version of javascript they are running ?

If I wanted to use functional programming in my web project which approach should I be using ? Should I include a library of functions or can I rely on the browsers implementations ?

Answer 1

You won’t be able to rely on the built-in implementations of these methods unless you know your userbase is 100% firefox 3.

However, you can code your implementations with the idea that they might already exist, as seen in the docs

if (!Array.prototype.map)
{
  Array.prototype.map = function(fun /*, thisp*/)
  {
    var len = this.length >>> 0;
    if (typeof fun != "function")
      throw new TypeError();

    var res = new Array(len);
    var thisp = arguments[1];
    for (var i = 0; i < len; i++)
    {
      if (i in this)
        res[i] = fun.call(thisp, this[i], i, this);
    }

    return res;
  };
}