Why does IE nuke window.ABC variables?

Question

When running the following block of code, FF and Chrome output typeof(hiya) = string while IE7/8 output typeof(hiya) = undefined.

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Answer 1

What you encountered is due to:

1. var being a statement
2. There's no block scope in JS
3. Statements get executed before the code runs

So what happens is that JavaScript will execute the var statement before before anything else, but it will not evaluate the assignment expression, therefor hiya will default to the value of undefined.

As Raynos already stated IE will execute each scripts on its own, therefore the behavior described above, will results in hiya being undefined.