JavaScript pre-allocated array Uncaught RangeError: Invalid Array Length

Question

I have a small loop of code which is throwing Uncaught RangeError: Invalid Array Length

I was able to reproduce it with just this in the Google Chrome console

const COUNT = 100_000_000;
const xValues = new Array(COUNT);
const yValues = new Array(COUNT);
for (let i = 0; i < COUNT; i++) {
    xValues[i] = i;
    yValues[i] = Math.sin(i * 0.000001);
}
console.log(`count: ${yValues.length}`);

Here's the output in developer console

As far as I know the maximum array size in Javascript is 2^32-1? There should be enough memory to allocate here and the index i is never negative or outside the bounds of the array as far as I can see.

Curiously enough, if I use this code, there is no crash

const COUNT = 100_000_000;
const xValues = new Array(COUNT);
const yValues = new Array(COUNT);
for (let i = 0; i < COUNT; i++) {
    xValues[i] = i;
    yValues[i] = i;
}
console.log(`count: ${yValues.length}`);

The value assigned to yValues[i] never goes outiside of the range -1, +1 so I can't see this as a number out of range problem either.

Anyone shed any light on this?

EDIT: Update

Another scenario that doesn't work. Computing a random walk.

    const count = 100_000_000;
    const xValues = new Array(COUNT);
    const yValues = new Array(COUNT);
    let prevYValue = 0;
    for (let i = 0; i < COUNT; i++) {
        const curYValue = Math.random() - .5;

        xValues[i] = i;
        yValues[i] = prevYValue + curYValue;

        prevYValue += curYValue;
    }

This one throws as well! But

    yValues[i] = i

is fine ¯\_(ツ)_/¯

EDIT: Update 2

Can now confirm this is browser specific, if you run the same test in firefox it works, but the browser asks you to wait.

Suspect the exception Uncaught RangeError is a badly reported timeout?

Interesting! It fails when i reaches 5,592,406 FYI (on my machine at least). — sp00m
– sp00m, Commented Dec 2, 2021 at 12:07
Chrome and Edge break both on the Math.sin() row when i === 5592406. If you start at 5592406 it breaks on 11184812 or (5592406 * 2), and the same for (5592406 * 3) ... — Andreas
– Andreas, Commented Dec 2, 2021 at 12:09
yValues[5592406] = Math.sin(5592406 * 0.000001) alone passes, so the RangeError does not seem to relate only to the number of indexes, but also somehow to the content being stored in the array? MDN doesn't make this behaviour explicit IMHO. — sp00m
– sp00m, Commented Dec 2, 2021 at 12:13
It is not related to computation. You get the same with just one array, and assigning a float to it, like 0.5. The difference in behaviour is clearly linked to the internal data type that is used for the array elements: either 32-bit integers or floats. See the difference in assigning 1e9 (is a 32-bit integer) or 1e10 (not a 32-bit integer). It is not related to calling Math.random or Math.sin. — trincot
– trincot, Commented Dec 2, 2021 at 14:17
Done, reported as a possible Chromium bug bugs.chromium.org/p/chromium/issues/detail?id=1275993 — Dr. Andrew Burnett-Thompson
– Dr. Andrew Burnett-Thompson, Commented Dec 2, 2021 at 15:33

Oleg Imanilov · Accepted Answer · 2021-12-02 16:18:06Z

9

The real reason is in V8 memory optimization. When you store integers - it stores the 32 bit number in place, But when you store double-number - it is stored differently (as an object) - so yValues array contains the reference but the actual value stored in heap. So in your example you just used all heap memory. To see the limit, use: console.memory and you'll see something like this:

MemoryInfo {
totalJSHeapSize: 10000000, 
usedJSHeapSize: 10000000, 
jsHeapSizeLimit: 3760000000}

In my browser it is 3_760_000_000

The object on heap takes 50+ bytes, so my limit somewhere around 69_000_000 floating point numbers.

answered Dec 2, 2021 at 16:18

Oleg Imanilov

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3 Comments

Dr. Andrew Burnett-Thompson Over a year ago

That's interesting, we found 2^26-1 to be the limit for indexes so approx 67108863 or lower worked. Strange that an array of doubles is stored as 50 bytes per value?!

Oleg Imanilov Over a year ago

It actually takes around 80 bytes per value in different places in memory :-) But sometimes optimized & takes less.

Dr. Andrew Burnett-Thompson Over a year ago

Curiously - if values are i32 format is there less memory? This is really interesting stuff, well worth the +upvotes if people have read this far ^_^

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