Javascript !instanceof If 语句

Javascript !instanceof If Statement

提问by ryandlf

This is a really basic question really just to satisfy my curiosity, but is there a way to do something like this:

这是一个非常基本的问题，只是为了满足我的好奇心，但是有没有办法做这样的事情：

if(obj !instanceof Array) {
    //The object is not an instance of Array
} else {
    //The object is an instance of Array
}

The key here being able to use the NOT ! in front of instance. Usually the way I have to set this up is like this:

这里的关键是能够使用 NOT ! 在实例前。通常我必须设置的方式是这样的：

if(obj instanceof Array) {
    //Do nothing here
} else {
    //The object is not an instance of Array
    //Perform actions!
}

And its a little annoying to have to create an else statement when I simply want to know if the object is a specific type.

当我只想知道对象是否是特定类型时，不得不创建一个 else 语句有点烦人。

回答by Sergio Tulentsev

Enclose in parentheses and negate on the outside.

用括号括起来并在外面否定。

if(!(obj instanceof Array)) {
    //...
}

In this case, the order of precedence is important (https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Operators/Operator_Precedence). The ! operator precedes the instanceof operator.

在这种情况下，优先顺序很重要（https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Operators/Operator_Precedence）。这 ！运算符在 instanceof 运算符之前。

回答by chrismichaelscott

if (!(obj instanceof Array)) {
    // do something
}

Is the correct way to check for this - as others have already answered. The other two tactics which have been suggested will not work and should be understood...

是检查这一点的正确方法 - 正如其他人已经回答的那样。建议的其他两种策略将不起作用，应该理解......

In the case of the !operator without brackets.

在!操作符没有括号的情况下。

if (!obj instanceof Array) {
    // do something
}

In this case, the order of precedence is important (https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Operators/Operator_Precedence). The !operator precedes the instanceofoperator. So, !objevaluated to falsefirst (it is equivalent to ! Boolean(obj)); then you are testing whether false instanceof Array, which is obviously negative.

在这种情况下，优先顺序很重要（https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Operators/Operator_Precedence）。该!运营商先于instanceof运营商。因此，!obj评估为falsefirst（相当于! Boolean(obj)）；那么您正在测试是否false instanceof Array，这显然是负面的。

In the case of the !operator before the instanceofoperator.

在!运算符之前的情况下instanceof。

if (obj !instanceof Array) {
    // do something
}

This is a syntax error. Operators such as !=are a single operator, as opposed to a NOT applied to an EQUALS. There is no such operator as !instanceofin the same way as there is no !<operator.

这是一个语法错误。诸如此类的!=运算符是单个运算符，而不是应用于 EQUALS 的 NOT。没有这样的运算符，就像!instanceof没有!<运算符一样。

回答by Wilt

It is easy to forget the parenthesis (brackets) so you can make a habit of doing:

很容易忘记括号（括号），因此您可以养成这样做的习惯：

if(obj instanceof Array === false) {
    //The object is not an instance of Array
}

or

或者

if(false === obj instanceof Array) {
    //The object is not an instance of Array
}

Try it here

在这里试试