Javascript Array flattenInPlace()

Array.fill = function(count, generator){
 var a = new Array(count)
 for(var i=0; i<count; i++){
  a[i] = generator(i)//from w ww. ja va  2  s .c om
 }
 return a
}

function isDefined(a){
 return (a !== null) && (a !== undefined)
}

Array.prototype.flattenInPlace = function(){
 var readIndex = 0,
  writeIndex = 0
 
 while(readIndex < this.length){
  var value = this[readIndex]
  
  if(isDefined(value)){
   this[writeIndex++] = this[readIndex++]
  } else {
   readIndex++
  }
 }

 this.length = writeIndex
}