函数，全局变量和局部变量 [英] Function, Global Variable, and Local Variable

问题描述

我不明白为什么测试后的x不会变成30但仍然保持10

I can't understand why the x after test won't become 30 but still remains 10

  <script>
        function test(){
            var x = 30;
            y = 40;
        }
    </script>


    <script>
        var x = 10;
        var y = 20;

        document.write("before test, x: " + x + ", y: " + y + "<br/><br/>");

        test();

        document.write("after test, x: " + x + ", y: " + y + "<br/><br/>");

    </script>

推荐答案

这是因为通过声明 var x = 30; ，您创建了一个名为 x 的变量

This is because by declaring var x = 30;, you create a variable named x that exists only in the function's scope.

但是，变量 y 仅在顶层定义.因此，当您运行函数 test 时，您将编辑本地 x 变量和全局(顶级)y y 变量.

The variable y, however, is only defined at top-level. So when you run the function test, you edit the local x variable, and the global (top-level) y variable.

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