'+ ='运算符在Javascript中做什么？ [英] What does the '+=' operator do in Javascript?

问题描述

运算符+ =是我在JavaScript中看到的很多，我完全不知道它是做什么的。有人可以简单地定义它是什么以及如何在JavaScript中使用它？我找到了这个例子，我不明白发生了什么。

The operator += is one that I have seen a lot in JavaScript and I have absolutely no idea what it does. Can someone simply define what it is and how I would use it in JavaScript? I found this example and I don't understand what is happening.

var message = "";
if (document.getElementById("x") == "") {
    message += "You must enter your last name."
}

推荐答案

这是一个赋值快捷操作符

It is an assignment shortcut operator

x + = y 表示 x = x + y

参见速记分配操作员表。

在javascript中 + 运算符也可以通过连接来处理字符串。所以在你的情况下它会添加到消息变量右边的字符串..

In javascript the + operator works on strings as well by concatenating them.. So in your case it will add to the message variable the string on the right side..

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