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javascriptclosuresundefinedreferenceerror

javaScript closures. Undefined value as input stops script. Sometimes

Playing with javascript closures I end up with this question I cannot reach to explain.

(function() {
    console.log("Inside closure"); //does not work
}(foo));

It does not work because foo is undefined. referenceError

But if prior I set var foo = undefined; it works (tested on Chrome and ff).

It is not the same to be undefined that to be set to undefined?

example in jsfiddle

Solution

  • In javaScript, 'undefined' is one of the primitive data types. It represents the type of an object. 

    var a = undefined;
var b;

console.log((typeof(a)));
console.log((typeOf(b)));

    The output will be undefined for both the cases.

    If you don't declare a variable at all and try to access it, the error thrown will be the following. I tried to access c which is not declared at all. Uncaught ReferenceError: c is not defined(…)