The order of declaration and initialization in JS

if inch window)) {  var a=1;  } alert (a);

Here's the alert coming out undefined

That's the equivalent of saying

var A; if inch window)) {   a=1;  } alert (a);

If the block is not scoped and therefore var a (declaration of the variable) is executed first, if the conditional statement is very clear is to determine whether a is the property of window, because the code snippet is not executed, because A=1 is the initialization of a does not execute, So the result of the following alert will be undefined.