Could you explain what does this code mean?

Question

let a;
let b=null;
let c=4;
let d='five';
let e=a||b||c||d;
alert(a);

/*
the output in text editor is undefined but I got this question from js quizes, the answer in quiz is 4
what is the correct answer and what does || mean?
*/

Answer 1

4 would not be the correct answer for what you've written here, but if the alert on js quizzes was for e, then it would be 4. a||b||c||d is setting e to the first variable that isn't false. || Means OR.

a is undefined and that is falsey in js. Same for b and null. c is the first value that isn't false, but if you change it to 0, you might get 'five' as the answer instead.