Race condition in JavaScript with compound assignment

Question

I\'m not talking about complex race conditions involving the network or events. Rather, I seem to have found out that the += operator is not atomic in V8 (Chrome 58

Answer 1

This is not a race condition, because you are explicitly yielding the execution using await.

The standard defines that a compound assignment such as += is not atomic: The left-hand-side of a compound assignment is evaluated before the right-hand-side.^[1]

So if your RHS changes acc somehow, the changes will be overwritten. Most simple example:

var n = 1;
n += (function () {
    n = 2;
    return 0;
})();

console.log(n);