设置后,全局变量未定义

Question

我试图运行这个代码,但它说a变量是undefined即使你可以看到我已经非常清楚地定义它,它必须是一个全局变量,因为它在每个循环后更改

var a = 1;
var b = 2;

window.setInterval(function(){
    alert(a);
    if(a == 1){
        document.getElementById('pic2').style.opacity = '1';
        document.getElementById('pic1').style.opacity = '0';
        var b = 1;
        var a = 2;
    }
    if(a == 2){
        document.getElementById('pic2').style.opacity = '0';
        document.getElementById('pic1').style.opacity = '1';
        var b = 2;
        var a = 1;
    }
}, 2000);

Answer 1

这是因为你要重新声明你的变量.从setInterval函数中删除变量可以解决此问题.

var a = 1;
var b = 2;

window.setInterval(function(){
    alert(a);
    if(a == 1){
        document.getElementById('pic2').style.opacity = '1';
        document.getElementById('pic1').style.opacity = '0';
        b = 1;
        a = 2;
    }
    if(a == 2){
        document.getElementById('pic2').style.opacity = '0';
        document.getElementById('pic1').style.opacity = '1';
        b = 2;
        a = 1;
    }
}, 2000);