这个语法到底在做什么？

Question

What is exactly happening in the following line?

return [selector, operation || "=", true];

I understand what returning is, the OR operator, etc. I've never seen this exact syntax.

Answer 1

It means:

Return an array of 3 elements: selector , operation (unless it's falsy , then "=" ), and true .

Answer 2

The line is parsed with the || operator binding tighter than the separating commas. So the line is equivalent to return [selector, (operation || "="), true];

In javascript, the || operator doesn't just work with boolean values. The actual semantics for return (a || b) is: "if (a is truthy ) return a; else return b;".

See: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_Operators#Logical_OR