I am editing someone's code and I don't understand what they are trying to do with this statement. This is at the end of the function.
return !(this.variable == "value")
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There's no reason to not use !=. Also, one should use !== and === when possible (almost always, usually).MaxArt– MaxArt2012-05-22 21:25:47 +00:00Commented May 22, 2012 at 21:25
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4 Answers
They're returning true or false based on the opposite of the result of the comparison.
It would probably have been clearer to write:
return this.variable != "value";
Sometimes you see:
return !!(some.expression);
which forces a "truthiness" conversion of the result of the expression to boolean (true or false). The "!!" is just a pair of individual logical complement ("not") operators. The first one (on the right) converts the result of the expression to boolean, but the opposite of the "truthiness". The second therefore flips it back.
4 Comments
Mark Reed
It would also have been better to use
=== (and !=== in your rewrite).
Pointy
Yes; without knowing what "this.variable" is, it's hard to say whether an "==" comparison would be correct. (It probably would be, but possibly not.)
Mark Reed
Nope. I never want a
== comparison. I'll coerce things explicitly if I want coercion, and leave off the relational entirely if I only care about Boolean interpretation.Pointy
Well @MarkReed, that's a fine thing if it's what you want to do, but not everybody codes that way.
this.variable == "value"
This compares two values and evaluates to a boolean (true if they compare equal).
!(this.variable == "value")
This negates the value (true <-> false).
return !(this.variable == "value")
This returns the value from the function.
Comments
They are checking this.variable is equal to "value" (which returns either true or false) and then using the ! (not) to make the value opposite.
It achieves the same result as
return (this.variable != "value")
You might as well change it to that because it is much clearer.
Comments
It's returning a true or false...
the exclamation point is a NOT...
so this.variable not equal to "value".
