Custom implementation of Array.push() as described by Douglas Crockford in his book "JavaScript: The Good Parts". The breakdown / analysis is my own.

custom-implementation-array-push.js

/* TL;DR:
 * The method replicates the functionality of Array.push
 * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/push
 * Array.method("myFunction", function() {}) is just an imaginary pre-implemented function that
 * is equivalent to Array.prototype.myFunction = function() {}
 */

Array.method('push', function() {

  // array.splice(start[, deleteCount[, item1[, item2[, ...]]]])
  // function.apply(thisArg, [argsArray])
  
  this.splice.apply(
    this, // thisArg
    [this.length, 0] // First to elements in argsArray, so they stand for 'start' and 'deleteCount'
      .concat(
        Array.prototype.slice.apply(arguments) // Create a clean array with the values we need to push out of the arguments passed to "push": item1, item2...
      ) // After the concat we will have something like [arrayLength, 0, item1, item2...]
  );

  // At this point, we are actually doing is:
  // this.splice.apply(theArrayAsThis, [arrayLength, 0, item1, item2...])
  // which is actually:
  // theArray.splice(arrayLength, 0, item1, item2...)

  return this.length; // Finally we have to return the new array length, just as the native push method does
});