Crazy Range Explain

range.js

// same things as ~~
// basically rounds to an integer (when x is a float)
// see: http://stackoverflow.com/questions/4055633/what-does-do-in-javascript
function doubleTilde(x) {
  if(x < 0) return Math.ceil(x);
  else return Math.floor(x);
}

function range(to, from, step) { 
  // set defaults
  var f = from || 1;  // (f=from||1)
  var s = step || 1;  // (s=step||1)

  // how far we're going to grab (range)
  // division means we may have a fraction...
  var r = (to - f) / s;    // ((to-(f=from||1))/(s=step||1))
  
  // round out the fraction
  r = doubleTilde(r);   // ~~((to-(f=from||1))/(s=step||1))
  
  // offset for users as arrays are zero indexed
  r += 1;                   // 1+~~((to-(f=from||1))/(s=step||1)))
  
  // give me a bunch of empty (undefined) object to placehold in the array
  var items = Array(r);
  
  // create an empty array the size of the range we are getting with the placeholder items
  var blankArray = Array.apply(0,items)

  // walk over the blank array (map) and perform the following function at each step
  // returns the mapped array
  return blankArray.map( function(e,i) {
    // i = the index of the item in the blank array
    // s = our step count
    // f = where we start from
    // 
    // so this is basically iterating over an empty array and filling in values offsetting by the "from"  param
    // we gave it and stepping as far as we told it in the "step" param
    return i*s+f;
  }); 
}

function range_orig(to, from, step) { 
  return Array.apply(0,Array(1+~~((to-(f=from||1))/(s=step||1)))).map( function(e,i){return i*s+f}); 
}

range(50, 0, 5);
range(50);

range_orig(50, 0, 5);
range_orig(50);