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Comments on Explaining the result of an arithmetic expression in JavaScript

Post

Explaining the result of an arithmetic expression in JavaScript

+1
−5

I misunderstand why the following code outputs -1 in console.

x = 42;
x = (x == 42) * -1 + (x != 42) * x;

-1

Due to Type Coercion, the comparison of x to 42 yields true and is thus translated to 1.

So 1 * -1 yields -1.

Now, (x != 42) which is false yields 0 so I have expected to get in console

-42

Because -1 + 0 * 42 MEANS -42.

So why did I get -1 in the end?

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2 comment threads

1 + 0 * 42 MEANS -42 ??? (4 comments)
Zero multiplied by anything is zero, so `0 * 42` is zero. Thus, `-1 + 0 * 42` is `-1 + 0` (because... (3 comments)
Zero multiplied by anything is zero, so `0 * 42` is zero. Thus, `-1 + 0 * 42` is `-1 + 0` (because...
hkotsubo‭ wrote over 2 years ago

Zero multiplied by anything is zero, so 0 * 42 is zero.

Thus, -1 + 0 * 42 is -1 + 0 (because of operator precedence rules, multiplication is made before the addition), which results in -1.

deleted user wrote over 2 years ago

Thank you, I believe this should be an answer.

Indeed, I thought addition primes multiplication there.

Operator precedence rules of JavaScript or of Math?

hkotsubo‭ wrote over 2 years ago · edited over 2 years ago