From Apress ProJavaScriptTechniques
In JavaScript, scope is kept within functions, but not within blocks (such as while, if, and for statements).
js 代码
-
- var foo = "test";
-
- if ( true ) {
-
-
- var foo = "new test";
- }
-
- alert( foo == "new test" );
-
- function test() {
- var foo = "old test";
- }
-
-
- test();
-
- alert( foo == "new test" );
An interesting aspect of browser-based JavaScript is that all globally scoped variables are actually just properties
of the window object.
js 代码
-
- var test = "test";
-
-
- alert( window.test == test );
In Listing 2-12 a value is assigned to a variable (foo) within the scope of the test() function. However, nowhere in Listing 2-12 is the scope of the variable actually declared (using var foo). When the foo variable isn’t explicitly defined, it will become defined globally, even though it is only used within the context of the function scope.
Listing 2-12
js 代码
-
- function test() {
- foo = "test";
- }
-
- test();
-
- alert( window.foo == "test" );
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