Question

Does JavaScript optimize the size of variables stored in memory? For instance, will a variable that has a boolean value take up less space than one that has an integer value?

Basically, will the following array:

var array = new Array(8192);
for (var i = 0; i < array.length; i++)
  array[i] = true;

be any smaller in the computer’s memory than:

var array = new Array(8192);
far (var i = 0; i < array.length; i++)
  array[i] = 9;

Answer 1

Short answer: Yes.

Boolean’s generally (and it will depend on the user agent and implementation) will take up 4 bytes, while integer’s will take up 8.

Check out this other StackOverflow question to see how some others managed to measure memory footprints in JS: JavaScript object size

Edit: Section 8.5 of the ECMAScript Spec states the following:

The Number type has exactly 18437736874454810627 values, representing the doubleprecision 64-bit format IEEE 754 values as specified in the IEEE Standard for Binary Floating-Point Arithmetic

… so all numbers should, regardless of implementation, be 8 bytes.