在 jquery 中查找数组的长度（大小）
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Find length (size) of an array in jquery
提问by Ed.
I think I'm going crazy. I have a simply question that I'm struggling with for some reason.
我想我快疯了。我有一个简单的问题，由于某种原因我正在努力解决。
Why does the below return 'undefined'?
为什么下面返回“未定义”？
var testvar={};
testvar[1]=2;
testvar[2]=3;
alert(testvar.length);
editI originally typed testvar[1].length. I knew this to be an error. I meant testvar.length
编辑我最初输入 testvar[1].length。我知道这是一个错误。我的意思是 testvar.length
回答by Cameron
Because 2isn't an array, it's a number. Numbers have no length.
因为2不是数组，而是数字。数字没有长度。
Perhaps you meant to write testvar.length; this is also undefined, since objects (created using the { ... }notation) do not have a length.
也许你打算写testvar.length；这也是未定义的，因为对象（使用{ ... }符号创建）没有长度。
Only arrays have a length property:
只有数组有长度属性：
var testvar = [ ];
testvar[1] = 2;
testvar[2] = 3;
alert(testvar.length); // 3
Note that Javascript arrays are indexed starting at 0and are not necessarily sparse(hence why the result is 3 and not 2 -- see this answerfor an explanation of when the array will be sparse and when it won't).
请注意，Javascript 数组从 开始索引0并且不一定是稀疏的（因此为什么结果是 3 而不是 2 - 请参阅此答案以了解数组何时稀疏以及何时不会稀疏）。
回答by mVChr
testvar[1] is the value of that array index, which is the number 2. Numbers don't have a length property, and you're checking for 2.length which is undefined. If you want the length of the array just check testvar.length
testvar[1] 是该数组索引的值，即数字 2。数字没有长度属性，您正在检查未定义的 2.length。如果你想要数组的长度，只需检查 testvar.length
回答by Dim_K
Integer has no method length. Try string
整数没有方法长度。尝试字符串
var testvar={};
testvar[1]="2";
alert(testvar[1].length);
回答by RafaSashi
If lengthis undefined you can use:
如果length未定义，您可以使用：
function count(array){
var c = 0;
for(i in array) // in returns key, not object
if(array[i] != undefined)
c++;
return c;
}
var total = count(array);
回答by kush
var mode = [];
$("input[name='mode[]']:checked").each(function(i) {
mode.push($(this).val());
})
if(mode.length == 0)
{
alert('Please select mode!')
};
回答by Tanmaya
var array=[];
array.push(array); //insert the array value using push methods.
for (var i = 0; i < array.length; i++) {
nameList += "" + array[i] + ""; //display the array value.
}
$("id/class").html(array.length); //find the array length.
回答by Tanmaya
obj={};
$.each(obj, function (key, value) {
console.log(key+ ' : ' + value); //push the object value
});
for (var i in obj) {
nameList += "" + obj[i] + "";//display the object value
}
$("id/class").html($(nameList).length);//display the length of
object.
