Differences between undefined
and null
undefined
means a variable has not been declared, or has been declared but has not yet been assigned a valuenull
is an assignment value that means “no value”- Javascript sets unassigned variables with a default value of
undefined
- Javascript never sets a value to
null
. It is used by programmers to indicate that a var has no value. undefined
is not valid in JSON whilenull
isundefined
typeof isundefined
null
typeof is anobject
. Why?- Both are primitives
- Both are falsy (
Boolean(undefined) // false, Boolean(null) // false
)
You can know if a variable is undefined
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You can check if a variable is null
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The equality operator considers them equal, but the identity doesn’t
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