Why can I delete a variable declared a = 1 and not one declared var b = 1 in javascript

Question

Let's suppose we are in the global scope:

When I declare a variable in JS:

a = 1

which I know is not the proper way (but it is not the question). I can use:

delete a (> returns true)

But when I declare:

var b = 1

I can't use:

delete b (> returns false)

Can anyone explain that behaviour?

What's the full code? One is a global variable (without var) while the other is local to the function it is declared in. — slebetman, Jan 20 '16 at 09:31

score 8 · Accepted Answer · answered Jan 20 '16 at 09:31

8

delete is only effective on an object's properties. It has no effect on variable or function names.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/delete

a becomes/is ultimately interpreted as window.a, while b clearly refers to a local variable.

answered Jan 20 '16 at 09:31

deceze

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That fact that you can access `b` through `window.b` too also adds to the confusion... – James Thorpe Jan 20 '16 at 09:33
2

Yeah, let's not get into that, or we'll all need a stiff drink... ;) – deceze Jan 20 '16 at 09:33

Why can I delete a variable declared a = 1 and not one declared var b = 1 in javascript

1 Answers1