如何检测一个变量是一个数组 [英] How to detect if a variable is an array

问题描述

什么是最好的事实标准跨浏览器的方法来确定在JavaScript中的变量是一个数组或不？

What is the best de-facto standard cross-browser method to determine if a variable in JavaScript is an array or not?

在搜索网络有许多不同的建议，一些好和相当多的无效

Searching the web there are a number of different suggestions, some good and quite a few invalid.

例如，下面是一个基本的方法：

For example, the following is a basic approach:

function isArray(obj) {
    return (obj && obj.length);
}

但是，请注意，如果数组是空的会发生什么，或者OBJ其实不是一个数组，但实现了一个length属性等。

However, note what happens if the array is empty, or obj actually is not an array but implements a length property, etc.

因此​​，这是执行最好在实际工作，是跨浏览器的，仍然有效地执行？术语

So which implementation is the best in terms of actually working, being cross-browser and still perform efficiently?

推荐答案

在JS对象的类型检查，通过做的instanceof ，即

Type checking of objects in JS is done via instanceof, ie

obj instanceof Array

如果对象跨越帧边界作为传递每一帧都有自己的阵列对象这是行不通的。您可以通过检查解决这个内部的 [等级] 的对象的属性。为了得到它，使用 Object.prototype.toString（）（这是保证由ECMA-262工作）：

This won't work if the object is passed across frame boundaries as each frame has its own Array object. You can work around this by checking the internal [[Class]] property of the object. To get it, use Object.prototype.toString() (this is guaranteed to work by ECMA-262):

Object.prototype.toString.call(obj) === '[object Array]'

这两种方法都将只对实际阵列和阵列没有状物体，如参数对象或节点列表工作。由于所有阵列状物体必须有一个数字长度属性，我会检查这些是这样的：

Both methods will only work for actual arrays and not array-like objects like the arguments object or node lists. As all array-like objects must have a numeric length property, I'd check for these like this:

typeof obj !== 'undefined' && obj !== null && typeof obj.length === 'number'

请注意，字符串将通过此检查，这可能会导致问题，因为IE浏览器不允许使用索引访问字符串的字符。因此，您可能需要更改 typeof运算的obj！= =未定义到 typeof运算的obj ===对象排除原语和主机对象有不同的类型，从对象产品总数。这将仍然让字符串对象通过，这将必须手动排除。

Please note that strings will pass this check, which might lead to problems as IE doesn't allow access to a string's characters by index. Therefore, you might want to change typeof obj !== 'undefined' to typeof obj === 'object' to exclude primitives and host objects with types distinct from 'object' alltogether. This will still let string objects pass, which would have to be excluded manually.

在大多数情况下，你居然想知道的是你是否可以通过数字通过索引对象进行迭代。因此，它可能是一个好主意，检查对象 0 不是命名的属性，可以通过这些检查之一来进行：

In most cases, what you actually want to know is whether you can iterate over the object via numeric indices. Therefore, it might be a good idea to check if the object has a property named 0 instead, which can be done via one of these checks:

typeof obj[0] !== 'undefined' // false negative for `obj[0] = undefined`
obj.hasOwnProperty('0') // exclude array-likes with inherited entries
'0' in Object(obj) // include array-likes with inherited entries

演员阵容到对象需要为阵列状的原语（即字符串）正常工作。

The cast to object is necessary to work correctly for array-like primitives (ie strings).

这里的code鲁棒检查JS数组：

Here's the code for robust checks for JS arrays:

function isArray(obj) {
    return Object.prototype.toString.call(obj) === '[object Array]';
}

和迭代（即非空）阵列状物体：

and iterable (ie non-empty) array-like objects:

function isNonEmptyArrayLike(obj) {
    try { // don't bother with `typeof` - just access `length` and `catch`
        return obj.length > 0 && '0' in Object(obj);
    }
    catch(e) {
        return false;
    }
}

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