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

为什么我使用它:(假设 i = 1 ）

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

divID = "question-" + i+1;

我得到问题-11 而不是问题-2 ？

推荐答案

请改用：

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

它是一个相当常见的问题，并不只是发生在JavaScript中。我们的想法是 + 可以代表两个连接和添加。

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

自+运算符将从左到右处理您的代码中的决策如下所示：

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

• question- + i ：因为问题 - 是一个字符串，我们将进行连接，导致question-1


• question-1+ 1 ：自queston- 1是一个字符串，我们将进行连接，产生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）它有所不同：

• 由于（i + 1）在括号内，其值必须在第一个之前计算可以应用+ ：
  
  
  
  
  • i 是数字， 1 是数字，所以我们会添加，导致 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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