null says there is absolutely nothing. undefined says there should be something but I have nothing. This is why the following function returns undefined when the argument is passed nothing because it means the function needs something but it has ...
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Purvi Barot
Software Engineer
undefined means a variable has been declared but has not yet been assigned a value.
var TestVar; alert(TestVar); //shows undefined alert(typeof TestVar); //shows undefinednull is an assignment value. It can be assigned to a variable as a representation of no value.
var TestVar = null; alert(TestVar); //shows null alert(typeof TestVar); //shows objectFrom the preceding examples, it is clear that undefined and null are two distinct types: undefined is a type itself (undefined) while null is an object.