Array.prototype.filter2

filter2.js

Array.prototype.filter2 = function(
  a, //a function to test each value of the array against. Truthy values will be put into the new array and falsey values will be excluded from the new array
  b, // placeholder
  c, // placeholder 
  d, // placeholder
  e // placeholder
) {
  c = this; // cache the array
  d = []; // array to hold the new values which match the expression
  for (e in c) // for each value in the array, 
    ~~e + '' == e && e >= 0 && // coerce the array position and if valid,
    a.call(b, c[e], +e, c) && // pass the current value into the expression and if truthy,
    d.push(c[e]); // add it to the new array
  
  return d // give back the new array
};