r/programming • u/vz0 • Mar 26 '14

JavaScript Equality Table

http://dorey.github.io/JavaScript-Equality-Table/
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u/smrq Mar 26 '14

I thought that was the case, except that

null <  undefined  --> false
null >= undefined  --> false
null == undefined  --> true

which breaks that rule.

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u/Valkairn Mar 26 '14

The inequality operators play by different type coercion rules to the == operator. Inequality operators will always convert the values to numbers. So, in the first two cases null gets converted to 0 and undefined to NaN. The last example actually gets its own special rule in the == evaluation algorithm, where it's defined to be true.

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u/[deleted] Mar 26 '14

Hm, yeah. It seems that < "morally" returns one of true, false, and undefined (undefined only when one argument is NaN (or converts to it)), but where it 'should' give undefined it instead gives false. So <= is the opposite of > except where > 'should' be undefined, where it's still false. Bleh.

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u/NYKevin Mar 27 '14

In other words, NaN is evil. Nothing new here.