Why does `true ||1 === 1/3` returns true in JavaScript?

Question

I know that the === operator is used to determine whether its both operands are equal and identical or not. That is to say that if left side operand has 1 then the right side operand must be 1 for returning true. but I don't get why javascript returns true for this calculation.

true || 1 === 1/3;

//true;

I don't get how this result can be true in JavaScript.

Since the first part of your assertion is `true` and the operator is `OR` the second part is never evaluated. (With `OR` the first true operand is returned) — Casimir et Hippolyte, Oct 02 '15 at 08:58
forgive me if u get this question boring for u. actually i'm very beggining js learner. — Ami Nirob, Oct 02 '15 at 08:58
Try this `alert(true || trash==good);` Nothing matters after that first `true` — Hanky Panky, Oct 02 '15 at 09:08

score 5 · Accepted Answer · edited May 23 '17 at 12:14

5

The === Operation will never be checked. The statement is true by true.

Also see this question and answer on how if statements are evaluated.

edited May 23 '17 at 12:14

Community

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answered Oct 02 '15 at 08:59

baao

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score 1 · Answer 2 · answered Oct 02 '15 at 08:58

1

|| means or. 'True or false' always evaluates to true.

answered Oct 02 '15 at 08:58

Jonah

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score 1 · Answer 3 · edited Oct 02 '15 at 09:34

1

1 === 1/3 is false

|| is OR

so your: true || 1 === 1/3; -> true OR false is true

edited Oct 02 '15 at 09:34

Aleksandr M

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answered Oct 02 '15 at 08:58

zucker

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score 1 · Answer 4 · edited Jun 20 '20 at 09:12

I know that === operator used to determine whether its both operands are equal and identical or not

is the "true" and "1/3" are equal and identical?

From the question and comment it seems that you're mistakenly thinking that the expression means

(true || 1) === 1/3;

true and 1/3 are indeed not equal and identical so the expected result would be false. But it doesn't, since || has lower precedence than ===. So it's parsed like this: true || (1 === 1/3);.

Logical expressions in Javascript (and most other C-like languages) are short-circuited, hence after the result is determined, the remaining expressions won't evaluated. That means the final result would be true

score 0 · Answer 5 · answered Oct 02 '15 at 08:59

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Your code boils down to this :

true || 1 === 1/3 (false)

or true || false

since the boolean operator || will return true if one of either conditions is true, you will end up with true.

answered Oct 02 '15 at 08:59

Timothy Groote

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Why does `true ||1 === 1/3` returns true in JavaScript?

5 Answers5