Posted on • Originally published at learn.coderslang.com
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In JavaScript, the typeof operator always returns a string.
So, even though typeof undefined evaluates to undefined, it’s a string and not the primitive undefined value.
The string ’undefined’ is not equal to the value undefined.
ANSWER: the message false will appear in the console.
For further actions, you may consider blocking this person and/or reporting abuse
Type is an everyday concept to programmers, but it’s surprisingly difficult to define it succinctly. I find it helpful to use Set as a conceptual model instead.
One extremely powerful typescript feature is automatic type narrowing based on control flow. This means a variable has two types associated with it at any specific point of code location: a declaration type and a narrowed type.
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Top comments (5)
So, typeof always returns a string and if we do a check like
it is actually checking whether the string undefined equal to the type undefined which is a false.
Instead if we do
we will get true as we are comparing with the string "undefined" and with the result which is a string we get from
typeof undefined.Yes, you're absolutely right
If
typeof(undefined) == undefined, that'd meanundefinedhas no type, so it makes sense for the string"undefined"to be returned instead :DHold on,
typeof nullis coming right after you :)Hey, I never claimed JavaScript is a sane language overall :D