Silly lib that executes a given callback when a variable is defined on window.

waitFor.js

/**
 * waitFor.js
 *
 * Silly lib that executes a given callback when a variable is defined on window.
 *
 * Matías Lescano | @mjlescano
 * Licensed under the MIT license
 */

;if( !window.waitFor ) (function(w){
  var rAF = w.requestAnimationFrame
         || w.mozRequestAnimationFrame
         || w.webkitRequestAnimationFrame
         || w.msRequestAnimationFrame
         || function(f){ return setTimeout(f, 25) }
  var watching = false
  var bars = []

  function watch(){
    var i = bars.length
    while( i-- ){
      var item = bars[i]
      if( window[item[0]] !== undefined ){
        bars.splice(i, 1)
        item[1].call(item[1])
      }
    }

    watching = bars.length ? rAF(watch) : false
  }

  window.waitFor = function waitFor(bar, cb){
    bars.unshift([bar, cb])
    if( !watching ) watching = rAF(watch)
  }
})(window);