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Asked: 2026-06-11T13:53:23+00:00

In my understanding defining a variable without the var keyword just evaluates to adding

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In my understanding defining a variable without the var keyword just evaluates to adding this variable to the window object. And on the other hand, trying to access a member of an object, that isn’t yet defined, evaluates to undefined. So I can do things like this:

> foo = "bar";
"bar"
> window.foo;
"bar"
> window.bar;
undefined

Why am I not able to get an undefined variables value (undefined) when accessing it directly?

> bar;
ReferenceError: bar is not defined

There is another thing that I don’t quite get, that I think could be related. When I type some literals into the console, they always evaluate to themselves. 1 evaluates to 1, [1] to [1] and so on. I always thought of a function to also be a literal because it has some value-like qualities (beeing first class citizen). But when I try to evaluate an anonymous function, I get a syntax error.

> function() {}
SyntaxError: Unexpected token (

I know that I can define a named function, but that evaluates to undefined (it defines the function somewhere rather then being it itself). So why arent functions literals?

thanks

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1 Answer

  1. Editorial Team

    For the first part of your question, see ReferenceError and the global object. Basically, explicitly referencing a non-existent property of an object will return undefined because there may be cases where you would want to handle that and recover. Referencing a variable that doesn’t exist should never happen, though, so it will fail loudly.

    For the second part of your question, you are trying to declare a function without a name, which isn’t possible. There’s a subtle difference between a function declaration and a function expression. Function expressions, for which the function name is optional, can only appear as a part of an expression, not a statement. So these are legal:

    var foo = function () { };

    (function () { });

    But not this:

    function () { };

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