Monkey Raptor

We can get DOM nodelist from querySelectorAll or getElementsByTagName or getElementsByClassName (new) method. The nodelist can't be "fully" processed like an array can.
We can loop through (read, and maybe set/write) the elements (using any of loop block methods), but there are methods which won't work for this object (it will return error code).

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Here's the basic idea
We need to create an empty array, then put the elements from the nodelist (array-like) to the (actual) empty array.
The newly created array will then be available for any of JavaScript array methods.

JavaScript snippet

Updated May 14, 2015

var NodeListToArray = function (a) { "use strict"; var i = 0, array = []; if (a instanceof Object) { do { array.push(a[i]); i += 1; } while (array.length < a.length); } return array; };

Snippet usage
var paragraph_nodelist = document.getElementsByTagName("p"), paragraph_array = NodeListToArray(paragraph_nodelist); // You can test the new array using: // console.log(paragraph_array instanceof Array); // It will return "true". Which means it is an [array] now. // ******************************* // To check the original nodelist: // console.log(paragraph_nodelist instanceof Array); // It will return "false", because it's an "Object".

There's a shorter way to do that using Array.prototype.slice.call(the_nodelist) as you may stumble on neat jQuery library.
More documentation of Array.prototype.slice.call(the_nodelist) at MDN

For example

Added May 14, 2015

var NodeListToArray = function (a) { "use strict"; if (a instanceof Object) { return Array.prototype.slice.call(a); } }; The same usage as the first snippet.