javascript - problem with an operator operation

Question

If neither n nor guard exists, n==null is true, and guard is undefined in the ternary operator. If the Boolean value is converted to false, it will be equal to n, that is, undefined is returned in the end. But why does it return 1? {code...}

仅有的幸福 · Answer

First of all, you misunderstood the order of operations

var test=function(array,n,guard){
    return (n==null || guard ? 1 : n); 
};
console.log(test([]));//1

The operation precedence of

|| (logical OR) is greater than that of the ternary operator

So (n==null || guard ? 1 : n) here first calculates the logical OR, and then calculates the ternary operator

Here it becomes true ? 1 : n
So output n
Attached is a picture of the priority of operations. I don’t remember which book I took it from

巴扎黑 · Answer

var test=function(array,n,guard){
    console.log(n==null);//true
    return (n==null || guard ? 1 : n); 
};
console.log(test([]));//1

||The priority is higher than trinocular, so it is (true || guard)? 1: n ===> true ? 1 :n