Invert array order

As other answers have already indicated, you can use reverse of the array. But note that this changes the original array, and there are times when you need to have a copy.

To avoid changing the original array, you can use slice before. This method is done to generate a new array that is a "slice" of the original. But if you pass 0 as the first argument, this slice will be a clone of the original whole array:

var meuArray = [1, 2, 5, 7, 9, 4];
var meuArrayInvertido = meuArray.slice(0).reverse();

Pedro, although Array.prototype.reverse works on your example will mutate the original array, so if you make a console.log(meuArray) you will notice that it will be inverted.

var output = document.getElementById("output")
var log = function (object) {
  var container = document.createElement("div");
  container.textContent = JSON.stringify(object);
  output.appendChild(container);
}

var meuArray = [1, 2, 5, 7, 9, 4];
log(meuArray);

var meuArrayInvertido = meuArray.reverse();
log(meuArray);

log(meuArrayInvertido);

<div id="output">
</div>

In this case it does not make much sense to instantiate a meuArrayInvertido object, since the original array was also inverted. so in this case you can use Array.prototype.map to do the work.

var output = document.getElementById("output")
var log = function (object) {
  var container = document.createElement("div");
  container.textContent = JSON.stringify(object);
  output.appendChild(container);
}

var meuArray = [1, 2, 5, 7, 9, 4];
log(meuArray);

var meuArrayInvertido = meuArray.map(function (item, indice, array){
  return array[array.length - indice - 1];
});
log(meuArray);

log(meuArrayInvertido);

<div id="output">
</div>

One way I found and using reverse

var meuArray = [1, 2, 5, 7, 9, 4];
var meuArrayInvertido = meuArray.reverse();
//meuArrayInvertido === [4, 9, 7, 5, 2, 1]

You can use a for cycle and make element elements change:

var array = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
alert(array);
var length = array.length;
var left = null;
var right = null;
for (left = 0, right = length - 1; left < right; left += 1, right -= 1) {
  var temporary = array[left];
  array[left] = array[right];
  array[right] = temporary;
}
alert(array);

(See here for comparing this method to .reverse() in terms of performance).

In terms of readability and complexity, if you are dealing with arrays small and inverted a few times, .reverse() is simpler. However, if the inversion performance is critical, use the method with the cycle.

As the TobyMosque replied, about the change in array , I developed another alternative for the occasion.

Define a function for the prototype Array , this function takes the this , which is nothing more than the variable of the type Array that calls the function, and with a for decreasing, using the function push() to creates a new array with the inverted order returning at the end of the function.

var arr = [1,2,3,4,5];

// Define uma função no prototipo do Array
// para retornar o mesmo com valores em orderm invertida.
Array.prototype.inverter = function() {
  var arr = [];
  for(i = this.length - 1; i >= 0; i--) {
     arr.push(this[i]);
  }
  return arr;
}

var nArr = arr.inverter();

// Saida de dados.
document.writeln(
  JSON.stringify(arr),
  JSON.stringify(nArr)
);