if块中这些代码之间的区别

由吥稀罕发布于 2020-04-09 07:38:22

我在这里得到了预期的结果。

 var modeObj = {};

array.forEach(num => {
    if (!modeObj[num])
        modeObj[num] = 0;
        modeObj[num]++;
});

我在这里得到空结果。

var modeObj = {};

array.forEach(num => {
    if (!modeObj[num]) {
        modeObj[num] = 0;
    }else {
        modeObj[num]++;
    }

});

上面的代码与下面的代码有什么不同？我在if条件中缺少一些概念。

紫涙嘫

2020-04-09 07:38:22

When you have if/else - the line inside the else block will only gets evaluated when the value of the if is false.

在第一个示例中-无论if是否有效，第二行都会每次运行。

If you don't have brackets - only the next line (after the if) is evaluated.
Your first example is actually the following:

var modeObj = {};

array.forEach(num => {
    if (!modeObj[num]) {
        modeObj[num] = 0;
    }
    modeObj[num]++;
});

娇气的小奶包

2020-04-09 07:38:22

The first code if condition does not have {}. Hence only the first line is executed and the line modeObj[num]++; is executed no matter what the result of the if condition is.

在第二个代码中，您添加了else。

小笨蛋o

2020-04-09 07:38:22

You're increasing modeObj[num]++ outside if part of the conditional & the second code snippet. It should be like so instead:

var modeObj = {};

array.forEach(num => {
    if (!modeObj[num]) {
        modeObj[num] = 0;
        modeObj[num]++;
    } else {
       // do something
    }

});

吥稀罕

这家伙很懒，什么都没留下

积分
0
话题
0
评论
3207
注册排名
1919