Javascript flatten array.

flat.js

var test = [[1,2,[3]],4];
var result = [];
//[1,2,3,4]

var process = function(arr) {
  arr.forEach(function(a){
    if(Array.isArray(a)){
      process(a);
    }else {
      result = result.concat(a);
    }
  });
}

process(test);
console.log(result);