Question

我有数组var john = ['asas','gggg','ggg'];

如果我在索引3处访问john，即。 john[3]，它失败了。

如何显示消息或警告，说明该索引没有值？

Answer 1

if (typeof yourArray[undefinedIndex] === "undefined") {
  // It's undefined
  console.log("Undefined index: " + undefinedIndex;
}

Answer 2

function checkIndex(arrayVal, index){
    if(arrayVal[index] == undefined){
        alert('index '+index+' is undefined!');
        return false;
    }
    return true;
}

//use it like so:
if(checkIndex(john, 3)) {/*index exists and do something with it*/}
else {/*index DOES NOT EXIST*/}

Answer 3

Javascript尝试抓住

try
  {
  //your code
  }
catch(err)
  {
  //handle the error - err i think also has an exact message in it.
alert("Error");
  }

Answer 4

Javascript数组从0开始。所以你的数组包含内容0 - 'asas'，1 - 'gggg'，2 - 'ggg'。

Answer 5

var john = ['asas','gggg','ggg'];
var index=3;
if (john[index] != undefined ){
 console.log(john[index]);
}

Answer 6

数组的索引从0开始，而不是1。

数组中有3个元素;他们是：

john[0] // asas
john[1] // gggg
john[2] // ggg

如何在JavaScript中记录数组索引？

6 个答案: