Is there a performance boost to predefining the length of a Javascript array when pushing items into that array?
For instance, suppose you're doing this:
var item1 = "apple",
item2 = "orange",
item3 = "sports car"; // Because I said so, that's why.
var myArray = []; // Empty array with initial length of 0
myArray.push(item1);
console.log(myArray.length) // 1
myArray.push(item2);
console.log(myArray.length) // 2
myArray.push(item3);
console.log(myArray.length) // 3
In the above code the length of myArray is recalculated on each push. Alternatively;
var item1 = "apple",
item2 = "orange",
item3 = "sports car";
var myArray = Array(3) // Assume we already know exactly how many items will be added
myArray[0] = item1;
console.log(myArray.length) // 3
myArray[1] = item2;
console.log(myArray.length) // 3
myArray[2] = item3;
console.log(myArray.length) // 3
My question is this, when you explicitly assign a value to a pre-existing slot within an array is the length property of that array still re-evaluated. If not, does sidestepping that process yield faster array population?
It should go without saying that this is more of a theoretical exercise than an actual real-world problem.
myArray[2] = item3;still the length will show 3 not 2, since the 3rd slot will take a default value