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var a,b;
(function(){ alert(a); alert(b); var a=b=3; alert(a); alert(b);})();alert(a);alert(b);Since a will be defined in local scope and b will be defined in global scope. Inside function both aand b are 3 but after function returns registered local variable (a) is deleted. Since b is defined in global scope it is not deleted.
var a=b=3Is the same as:
var a = (b = 3)And var statement applies only to a, and not to b. You can check the syntax of var statementhere.
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原文地址：http://www.cnblogs.com/michael-xiang/p/4645289.html
