Swapping two arrays seems to behave asynchronous outside function #11047
Description
Version: v7.1.0
Platform: Windows 8.1; 64-bit
Issue details: Swapping two variables from a function sometimes behaves like it is asynchronous as seen from outside that function, but synchronous from inside. It only happens when variables are swapped using the following short syntax:
[a, b] = [b, a];
However, it doesn't hapen every time. This is an example
'use strict';
var a = [];
var b = [];
var c = () => a;
var d = () => [a, b] = [b, a];
d();
console.log(a === c()); // Sometimes it prints `false`, which should be impossible
However, it doesn't work always. But, after a few hours of testing, I came up with the following code, which always prints wrong output:
'use strict';
// Here if I change `const` to `var` it prints 111
const w = 100;
const h = 100;
var first = new Array(100).fill(0).map(() => new Uint8Array(100));
var second = new Array(100).fill(0).map(() => new Uint8Array(100));
var getFirst = () => first;
var x, y;
var beginning = true;
var i = 0;
var func = () => {
if(beginning){
beginning = false;
// If I remove bitwise `or` operator from here, it prints 111
for(y = 0; (y | 0) < (h | 0); y++) for(x = 0; (x | 0) < (w | 0); x++){}
}else{
for(y = 0; y < h; y++) for(x = 0; x < w; x++){
// If I change the number 1 to 0 from this line, it prints 111
if((first[x | 0][y | 0] | 0) + 1);
}
[first, second] = [second, first];
}
console.log(first === getFirst() ? 1 : 0); // It should always print 1, but third time it prints 0
};
func(); // Prints 1, that is ok
func(); // Prints 1 too, its ok
func(); // This one always prints 0
Here is how output looks like. I cannot find any possible explanations why is zero here: