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I just discovered that Javascript has typed arrays via this link. I was immediately curious what the benefit of such objects might be in the language.

I noticed that UInt8Arrays lose the .map()-type functions that I would have for normal arrays objects so if you want to loop over them you would need a for loop.

I assumed that I might be able to expect some performance boost when using UInt8Arrays but this doesn't seem to be the case.

var a = d3.range(225)
var b = new Uint8Array(d3.range(225))

console.time("a")
var result = 0;
for (var j = 10000; j >= 0; j--) {
    for (var i = a.length - 1; i >= 0; i--) {
        result += a[i];
    };
};
console.timeEnd("a")
console.time("b")
var result = 0;
for (var j = 10000; j >= 0; j--) {
    for (var i = b.length - 1; i >= 0; i--) {
        result += b[i];
    };
};
console.timeEnd("b")

I am using the d3 library to quickly generate a large array. This script gives the following output:

a: 2760.176ms
b: 2779.477ms 

So the performance doesn't improve. The UInt8Array also doesn't throw an error when you insert a wrong value.

> new Uint8Array([1,2,3,4,'aasdf'])
[1,2,3,4,0]

With this in mind, what is the proper use case for UInt8Array in Javascript? It seems like the normal array is a lot more flexible, equally robust and equally fast.

I just discovered that Javascript has typed arrays via this link. I was immediately curious what the benefit of such objects might be in the language.

I noticed that UInt8Arrays lose the .map()-type functions that I would have for normal arrays objects so if you want to loop over them you would need a for loop.

I assumed that I might be able to expect some performance boost when using UInt8Arrays but this doesn't seem to be the case.

var a = d3.range(225)
var b = new Uint8Array(d3.range(225))

console.time("a")
var result = 0;
for (var j = 10000; j >= 0; j--) {
    for (var i = a.length - 1; i >= 0; i--) {
        result += a[i];
    };
};
console.timeEnd("a")
console.time("b")
var result = 0;
for (var j = 10000; j >= 0; j--) {
    for (var i = b.length - 1; i >= 0; i--) {
        result += b[i];
    };
};
console.timeEnd("b")

I am using the d3 library to quickly generate a large array. This script gives the following output:

a: 2760.176ms
b: 2779.477ms 

So the performance doesn't improve. The UInt8Array also doesn't throw an error when you insert a wrong value.

> new Uint8Array([1,2,3,4,'aasdf'])
[1,2,3,4,0]

With this in mind, what is the proper use case for UInt8Array in Javascript? It seems like the normal array is a lot more flexible, equally robust and equally fast.

• javascript
• arrays

Share Improve this question Follow edited Oct 11, 2014 at 21:40 Dan D. 74.7k1515 gold badges110110 silver badges127127 bronze badges asked Oct 11, 2014 at 21:39 cantdutchthiscantdutchthis 34.7k1717 gold badges7777 silver badges116116 bronze badges 3

• 1 Read this: developer.mozilla/en-US/docs/Web/JavaScript/Typed_arrays. A main use is for dealing with raw binary data that es from the outside world that you want to access in javascript. – jfriend00 Commented Oct 11, 2014 at 21:42
• 1 If a piler can verify that all the members of a typical Array will always be of the same type, it can optimize to use a typed array. Do this before you run the test: a[0] = null. In a mathematical operation, null will be treated as 0, but it makes a very large difference in the timed result. On my machine, it goes from about 5ms to about 47ms. – user1106925 Commented Oct 11, 2014 at 21:50
• I've used them in WebGL and WebSockets, both for dealing with binary data "as is" without having to bring into "native" JavaScript arrays. – Adam Commented Jan 30, 2015 at 20:50

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1 Answer 1

Sorted by: Reset to default 16

"Performance" usually doesn't mean just how fast your script runs. There are also many other important factors, like how fast it freezes your pc and/or crashes. memory. The smallest amount of memory javascript implementation usually allocate for a var is 32 bit. This means

var a = true;

a boolean looks like this in your memory:

0000 0000 0000 0000 0000 0000 0000 0001

It's a huge waste, but usually not a problem, as no one uses a significant enough amount of them for it to really matter. Typed Arrays are for cases where it does matter, when you can actually reduce your memory usage by a huge amount, like when working with image data, sound data, or all sorts of raw binary data.

Another difference, that allows you to potentially save even more memory in some cases is that it allows you to operate on data passed by reference you'd normally pass by value.

Consider this case:

var oneImage = new Uint8Array( 16 * 16 * 4 );
var onePixel = new Uint8Array( oneImage.buffer, 0, 4 );

you now have 2 independent views on the same ArrayBuffer, operating on the same data, applying that concept allows you to not only have that one huge thing in your memory, it allows you to actually subdivide it into as many segments as you currently want to work on with little overhead, which is probably even more important.

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