javascript - What does `var` do in the global scope? -

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this question has answer here:

in html <script> tag, outside of function, var have meaning?

is there difference between these 3 notations?

<script>   var = 1;   b = 1;   window.c = 1; </script>

at top level (outside functions) var declares global variable.

to avert this, wrap code in function.

(function () {     var = 1; }());  'a' in window; // => false

despite each form declares global variable, have subtle differences. var creates undeletable property on window, , subject typical hoisting rules whereby property exist on window @ start of var statement's execution context. other forms create deletable property on window @ time line of code executed.

see this answer more info.


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