Javascript (+) 符号连接而不是给出变量的总和 [英] Javascript (+) sign concatenates instead of giving sum of variables

问题描述

为什么当我使用它时:(假设 i = 1)

Why when I use this: (assuming i = 1)

divID = "question-" + i+1;

我得到的是 question-11 而不是 question-2?

I get question-11 and not question-2?

推荐答案

改用这个:

var divID = "question-" + (i+1)

这是一个相当普遍的问题，不仅仅发生在 JavaScript 中.这个想法是 + 可以表示 连接和加法.

It's a fairly common problem and doesn't just happen in JavaScript. The idea is that + can represent both concatenation and addition.

由于 + 运算符将从左到右处理，因此您的代码中的决定如下所示:

Since the + operator will be handled left-to-right the decisions in your code look like this:

• "question-" + i:由于"question-"是一个字符串，我们将进行连接，结果是"question-1"
• "question-1" + 1:由于"queston-1"是一个字符串，我们将进行连接，结果是"question-11".

• "question-" + i: since "question-" is a string, we'll do concatenation, resulting in "question-1"
• "question-1" + 1: since "queston-1" is a string, we'll do concatenation, resulting in "question-11".

使用 "question-" + (i+1) 就不同了:

• 由于 (i+1) 在括号中，因此必须在应用第一个 + 之前计算其值:
  • i 是数字，1 是数字，所以我们做加法，得到 2
  • since the (i+1) is in parenthesis, its value must be calculated before the first + can be applied:
    • i is numeric, 1 is numeric, so we'll do addition, resulting in 2

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