When to use Float32Array instead of Array in JavaScript

Question

When does it make sense to use a Float32Array instead of a standard JavaScript Array for browser applications?

This performance test shows Float32Array to be, in general, slower - and if I understand correctly a standard Array stores numbers as 64bit - so there is no advantage in precision.

Aside from any possible performance hit, Float32Array also has the disadvantage of readability - having to use a constructor:

a = new Float32Array(2); a[0] = 3.5; a[1] = 4.5; 

instead an array literal

a = [3.5, 4.5]; 

I'm asking this because I'm using the library glMatrix which defaults to Float32Array - and wondering if there's any reason I shouldn't force it to use Array instead which will allow me to use array literals.

Answer 1

I emailed the developer of glMatrix and my answer below includes his comments (points 2 & 3):

1. Creating a new object is generally quicker with Array than Float32Array. The gain is significant for small arrays, but is less (environment dependent) with larger arrays.

2. Accessing data from a TypedArray (eg. Float32Array) is often faster than from a normal array, which means that most array operations (aside from creating a new object) are faster with TypedArrays.

3. As also stated by @emidander, glMatrix was developed primarily for WebGL, which requires that vectors and matrices be passed as Float32Array. So, for a WebGL application, the potentially costly conversion from Array to Float32Array would need to be included in any performance measurement.

So, not surprisingly, the best choice is application dependent:

• If arrays are generally small, and/or number of operations on them is low so that the constructor time is a significant proportion of the array's lifespan, use Array.

• If code readability is as important as performance, then use Array (i.e. use [], instead of a constructor).

• If arrays are very large and/or are used for many operations, then use a TypedArray.

• For WebGL applications (or other applications that would otherwise require a type conversion), use Float32Array (or other TypedArray).