What is the difference between the two array structures and their repetition loops in Javascript?

Question

I would like to know which is the best way to work with arrays?

var meu_array = new Array(1, 2, 3);
var meu_array = [1, 2, 3];

There is some difference in performance between the 6 cases presented in the use of loop below?

 // foreach 
    meu_array.forEach(function(valor, i){
        console.log(valor, i);
    }); 
 // for key associativa
    for (var i in meu_array) {
        console.log(meu_array[i], i);
    }
 // for valor associativo  
   var i = 0;
   for (value of meu_array) {
       console.log(value, i++);
   }
 // for interator
    for (var i=0; i<=meu_array.length; i++) {
        console.log(meu_array[i], i);
    }
 // while
    var i=0;
    while (i <= meu_array.length) {
          console.log(meu_array[i], i);
     i++;
    }
 // jquery
    $.each(meu_array, function(i, value) {
      console.log(value, i);
    });

Answer 1

Essentially it makes no practical difference. They create the same array and the performance will be the same for him. The performance may be a little better for the first case, but only in creation and it will be very little difference to care about. And this depends on language implementation. Don’t count on this.

There is a difference in performance by the algorithm used in each exemplified situation, but not because the array was created one way or another.

The first way is considered confusing, because if you want to create a array with only one element, it will not do what you expect. It will create a array with the specified amount of elements and not a array with an element of that value.

In addition she will call the builder who will build the array. The second way will create the array without going through the constructor. This may seem to give in it. But there are no guarantees in the language that this is true. It is possible to override the method.

The general recommendation is not to use the Array() unless you really need it and you know what you’re doing and why you’re choosing it.