在JavaScript中查找变量类型 [英] Finding Variable Type in JavaScript

问题描述

在Java中，您可以对变量使用 instanceOf 或 getClass（）来查找其类型。

In Java, you can use instanceOf or getClass() on a variable to find out its type.

如何在JavaScript中找出不是强类型的变量类型？

How do I find out a variable's type in JavaScript which isn't strongly-typed?

例如，我怎么知道栏是布尔还是数字，或字符串？

For example, how do I know if the bar is a Boolean or a Number, or a String?

function foo(bar) {
    // what do I do here?
}

推荐答案

使用 typeof ：

> typeof "foo"
"string"
> typeof true
"boolean"
> typeof 42
"number"

所以你可以这样做：

if(typeof bar === 'number') {
   //whatever
}

小心但是如果用它们的对象包装器定义这些原语（你永远不应该这样做，尽可能使用文字）：

Be careful though if you define these primitives with their object wrappers (which you should never do, use literals where ever possible):

> typeof new Boolean(false)
"object"
> typeof new String("foo")
"object"
> typeof new Number(42)
"object"

数组的类型仍然是物体。在这里，你真的需要 instanceof 运营商。

The type of an array is still object. Here you really need the instanceof operator.

更新：

另一种有趣的方式是检查 Object.prototype.toString ：

Another interesting way is to examine the output of Object.prototype.toString:

> Object.prototype.toString.call([1,2,3])
"[object Array]"
> Object.prototype.toString.call("foo bar")
"[object String]"
> Object.prototype.toString.call(45)
"[object Number]"
> Object.prototype.toString.call(false)
"[object Boolean]"
> Object.prototype.toString.call(new String("foo bar"))
"[object String]"
> Object.prototype.toString.call(null)
"[object Null]"
> Object.prototype.toString.call(/123/)
"[object RegExp]"
> Object.prototype.toString.call(undefined)
"[object Undefined]"

With您不必区分原始值和对象。

With that you would not have to distinguish between primitive values and objects.

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