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Asked: 2026-06-16T00:40:04+00:00

I was just testing the in operator in Javascript. When I run something like

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I was just testing the in operator in Javascript. When I run something like console.log("cookie" in document), it logs true, but when I do console.log("cookie" in "cookiejar") or assign cookiejar to a variable a and then do console.log("cookie" in a), I get an error statement TypeError: invalid ‘in’ operand a. Can anyone tell me why is it behaving like this?

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1 Answer

  1. Editorial Team

    The in operator doesn’t do what you think it does. a in b tells you if a given object b has the property named a.

    You cannot use in to search for characters in a string. Use indexOf for that.

    'cookiejar'.indexOf('cookie')

    Note that the in operator is entirely separate from and completely unrelated to the for-in statement.

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