How come this is true?

Question

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Why does (0 < 5 <3) return true?

How come this is true?:

console.log(100 < 210 < 200); // outputs true

see: [http://meta.stackexchange.com/questions/92074/what-can-i-do-when-getting-it-does-not-meet-our-quality-standards] — 4b0, Aug 21 '11 at 08:56

score 3 · Answer 1 · answered Aug 21 '11 at 08:44

That's equivalent to:

console.log((100 < 210) < 200);

which is equivalent to:

console.log(true < 200);

And this evaluates to true because when using operators like <, true is treated as if it were a 1

Consequently, the following will evaluate to false:

console.log(true < 0)

score 2 · Answer 2 · answered Aug 21 '11 at 08:44

100 < 210 < 200 is equivalent to (100 < 210) < 200 which is true < 200 which is 1 < 200 which is true.

That last bit (true becoming 1) may be a bit surprising. It's the result of how JavaScript does relational operations (Section 11.8.5 of the spec), which says amongst other things that if the relation is between a non-number (other than null or undefined) and a number, you convert the non-number to a number, and the conversion of true to a number results in 1 (Section 9.3 of the spec.)

How come this is true?

2 Answers2