Why does operator precedence works other way with variable assignment in Javascript

Question

I have a code like this.

let y = 2;
y *= 3+4;

The above line is a short hand of y = y*3+4. So as per the precedence level, * should take a precedence. So i am expecting a calculation like this, (2*3)+4 so that should return 10. But why does it executes this way 2*(3+4) and returned 14. Can somebody explain in detail?

Answer 1

It's helpful to see how the JS parser interprets that statement: https://esprima.org/demo/parse.html?code=y%20*%3D%203%2B4

Binary expressions are evaluated before assignment expressions.

The + is a binary expression that has 3 and 4 as operands.

The *= is an assignment expression that has, on the left hand side, y, and on the right hand side, the result of the binary expression (3 + 4, or 7).