What does [literal] in [array/object] mean?

Question

What does the following syntax mean:

1 in [1,2,3,5]

I know it doesn\'t search for 1 in the array. But what does it do?

I\'ve seen it u

Answer 1

Very simply, it's an object property search:

print ('a' in {'a':1, 'b': 2}); // true
print ('c' in {'a':1, 'b': 2}); // false

Live demo.

This is subtly different to the similar use of in in for loops.

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Also note that it should not be used with arrays, although this is a common error to make.

It is unspecified what properties besides numeric keys make up the internals of an array, so you should stick to the Array API (e.g. indexOf) if you're using Arrays, otherwise you'll end up with behaviour that you may not expect:

print ('length' in [1,2,3,4]); // true