Why does comparison statement of three variables in JavaScript return false?

Question

var data = {
  name: 'home',
  href: '/'
};
var pathname = "/";
console.log(data.href == pathname == "/")

The console.log statement printed "false".

However, if I have the following:

var data = {name: 'home', href: '/'};
var pathname = "/";
console.log(data.href == "/");
console.log(data.href == pathname);
console.log(pathname == "/");

All three of the console.log statement will print true.

Left-to-right evaluation... consider `true === "/"` – Phil Aug 10 '22 at 04:12 — Phil, Aug 10 '22 at 04:12

score 1 · Accepted Answer · answered Aug 10 '22 at 04:13

1

The comparison operator == is evaluated left to right. ^ref

data.href == pathname == "/"

becomes

true == "/"

which is false.

answered Aug 10 '22 at 04:13

Louys Patrice Bessette

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score 0 · Answer 2 · edited Aug 17 '22 at 05:44

console.log(data.href == pathname == "/")

All three elements may be the same, but that's not what is being compared here.

Take the second and third elements. Both are /, so the result of the comparison is true. This is compared with the first element, but / is not true so the comparison fails.

The exact order of evaluation doesn't matter here. The first comparison returns a boolean, so the second comparison returns false.

Why does comparison statement of three variables in JavaScript return false?

2 Answers2