Question

我的javascript代码如下：

<script type="text/javascript">
    var team = [{id:"1", name:"chelsea"}, {id:"3", name:"mu"}, {id:"5", name:"arsenal"}];
    for(var i = 0; i < 5; i++) {
        if(team[i].id || typeof team[i].id !== 'undefined' || team[i].id !== null) {
            console.log(team[i].id)
        }
        else {
            console.log(i+1)
        }
    }
</script>

如果代码运行，则在控制台上存在如下错误：

未捕获的TypeError：无法读取属性＆＃39; id＆＃39;未定义的

如果变量不存在我添加了条件

我该如何解决？

Answer 1

据我所知，当你在评论输出1,2,3,4,5上说你需要缺少的ID时 - 在你的情况下有2,4

＆＃13;

var team = [{id:"1", name:"chelsea"}, {id:"3", name:"mu"}, {id:"5", name:"arsenal"}];
var empty_ids = 0;
for(var i = 0; i < 5; i++) {   
    if(team[i] && typeof team[i] !== 'undefined' && team[i] !== null) {  
        if(parseInt(team[i].id) !== i + 1){  // check if id on the array not equal the i + 1 from the loop
          for( var k= 1 ; k < parseInt(team[i].id) - empty_ids ; k++){ 
            console.log(empty_ids + k +" missing");
          }
          console.log(team[i].id);
        }else{
          console.log(team[i].id);
        }
        empty_ids = parseInt(team[i].id);
    }else{
      if(empty_ids <= i){
        console.log(empty_ids + 1 + " undefined team[i]");
        empty_ids = empty_ids + 1;
      }
      
    }
}

＆＃13;

注意：即使您更改了团队数组

，此代码仍然有效

var team = [{id:"1", name:"chelsea"}, {id:"5", name:"arsenal"}]; 
//or 
var team = [{id:"1", name:"chelsea"}, {id:"3", name:"mu"}, {id:"4", name:"arsenal"}]; 
//or 
var team = [{id:"1", name:"chelsea"}, {id:"4", name:"arsenal"}];

因此，请尝试使用建议值更改var team =。我添加了missing和undefined，以便您注意console.log来自哪里

Answer 2

很少有观察，

而不是for循环中的硬编码值'5'，你应该使用数组长度，即在这种情况下是team.length
而不是记录'i + 1'你可以记录'i'作为数组索引从'0'开始。或者只是你可以打印对象/团队名称。

这里是修改后的代码，

<script type="text/javascript">
    var team = [{id:"1", name:"chelsea"}, {id:"3", name:"mu"}, {id:"5", name:"arsenal"}];
    for(var i = 0; i < team.length; i++) {
        if(team[i].id || typeof team[i].id !== 'undefined' || team[i].id !== null) {
            console.log(team[i].id)
        }
        else {
            console.log('team id not found for index ' + i);
        }
    }
</script>

Answer 3

主要问题是你正在检查一个对象的属性，在本例中是team [i]，可能是未定义的。

例如，如果你是console.log（团队[4]），它将指向未定义，因为团队中只有3个对象。检查未定义的属性将导致错误。

＆＃13;

var arr = [1,2,3]

// this will be undefined
var element = arr[4]

console.log(element.toString)

＆＃13;

所以，您还应检查team [i]是否未定义。您的代码应该类似于下面的代码。我假设您要打印1,2,3,4,5。

＆＃13;

var team = [{id:"1", name:"chelsea"}, {id:"3", name:"mu"}, {id:"5", name:"arsenal"}];

for(var i = 0; i < 5; i++) {
    // check if team[i] is not undefined using (team[i] !== undefined)
    if((team[i] !== undefined) && ( team[i].id || typeof team[i].id !== 'undefined' || team[i].id !== null)) {
        var currentId = team[i].id > i + 1 ? i + 1 : team[i].id;
        console.log(currentId)
    }
    else {
        console.log(i + 1);
    }
}

＆＃13;

如何在javascript中检查对象数组中的索引是否存在？

3 个答案: