Javascript-全局变量和全局范围内的变量是否不同（在jsfiddle中）？

Question

Are global variables and variables in global scope different? Please see the code below or the JSfiddle implementation - http://jsfiddle.net/2ngj9rqa/ .

a = 10;
var b = 20;

function x() {
a = 20;
}

alert(window.a);
alert(window.b);

Answer 1

that's a trick in JSFiddle, b is wrapped in onload but not window if you choose no wrap , it's fine. Also try the same in plunker is fine.

Answer 2

The code you've written will work fine in all major browsers.It won't work because it is wrapped by onload in jsfiddle.Both a and b are global variables here and both of them are in global scope. You can access them from anywhere in your code unless you introduce a variable with same name inside a function's own scope.There is something called variable scoping and hoisting.All the variables(except implicit global) are hoisted at the top of its scope when you declare a variable or assign value to it( with var keyword ofcourse ) . know more on variable and function hoisting So,your code is equivalent to this:

var b;

a = 10;
b = 20;

function x() {
a = 20;
}

alert(window.a);
alert(window.b);