// [[1,2,[3]],4]

var arr = arrayFlatten([[1,2,[3]],4,[1,[2,[3]]]]);
console.log(arr);

//Main function
function arrayFlatten(obj){
	var flattenArray=[];
  //Call recursive funcion sending the array as "reference"
  flatten(obj,flattenArray);
  return flattenArray;
}

function flatten(obj, flattenArray){
	//If is an array, go for each element and call the same recursive function
	if(isArray(obj)){
  	obj.forEach(function(item){
    		flatten(item,flattenArray);
    });
  }
  else{
  	//is an integer, just push in the array
  	flattenArray.push(obj);
  }
}

function isArray(obj) {
		//Check if the object is an array
    return Object.prototype.toString.call(obj) === '[object Array]';
}