CODEWITHSUNDEEP
javascript
goodvibration
goodvibration

Reputation: 6206

Does the Javascript standard guarantee a deterministic result for ~0?

Sorry if this is a duplicate question; was unable to find an answer anywhere.

Does the Javascript standard guarantee a deterministic result for ~0?

Chrome gives me -1 for <script>alert(~0);</script>.

Is this result guaranteed cross-browser (and cross-platform in general)?

Upvotes: 1

Views: 112

Answers (2)

thefourtheye
thefourtheye

Reputation: 239643

The specification says,

  1. Let expr be the result of evaluating UnaryExpression.
  2. Let oldValue be ToInt32(GetValue(expr)).
  3. Return the result of applying bitwise complement to oldValue. The result is a signed 32-bit integer.

The first step actually evaluates the expression. Second step converts the expression to a 32 bit integer. All implementations should implement this properly. The third step is simply to flip the bits in the number. There is only one way to do this.

So I would expect all the implementations to give the same result.

Upvotes: 2

Barmar
Barmar

Reputation: 782148

Yes, it's deterministic. From the MDN documentation of bitwise NOT

Bitwise NOTing any number x yields -(x + 1).

This is because the bitwise operators are based on two's complement notation.

Upvotes: 2

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