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  • Counterintuitive native array methods behavior (.length > 2^32)

Counterintuitive native array methods behavior (.length > 2^32)

# Michał Wadas (9 years ago)

Steps to reproduce:

let p = {
0: 'a',
1: 'b',
2: 'c',
length: Math.pow(2,32)+1
};
Array.prototype.forEach.call(p, (el)=>console.log(el)); // logs only 'a'

The cause of this behaviour is obvious for anyone that reads specification - every native Array.prototype methods perform abstract operation `ToUint32(this.length).

Anyway - this behaviour obviously counters intuition. I think it would be totally OK to allow native methods to throw when .length > 2^32,

# Ivan Vyshnevskyi (9 years ago)

I believe, it's fixed in ECMAScript 2015: now check for length being < 2^32 is performed only on array creation [1], and < 2^53 when length is going to be updated [2].

See, for example, current algorithm of Array.prototype.forEach: www.ecma-international.org/ecma-262/6.0/#sec-array.prototype.foreach

[1]: step 3 of ArrayCreate www.ecma-international.org/ecma-262/6.0/#sec-arraycreate

[2]: for example step 7 of Array.prototype.push www.ecma-international.org/ecma-262/6.0/#sec-array.prototype.push