JavaScript中的++ i和i ++有什么区别 [英] What's the difference between ++i and i++ in JavaScript

问题描述

在寻求学习和改进JavaScript的过程中，我遇到了一个带有switch/case语句的脚本，我注意到使用++在++之前加上一些变量，然后在++之后加上一些变量.变量.这些有什么区别?这是我要解释的示例，请注意m和y变量.

on my quest to learn and improve my JavaScript I came across a script that has a switch / case statement and I noticed some variables are incremented using ++ with the variable before the ++ and then some variables have the ++ after the variable. What's the difference between these? Here's an example of what I'm trying to explain notice the m and y variables.

 switch(f){
        case 0:{

            ++m;
            if(m==12){
                m=0;
                y++;
            }
            break;
        }
        case 1:{

            --m;
            if(m==-1){
                m=11;
                y--;
            }
            break;
        }
        case 2:{

            ++y;
            break;
        }
        case 3:{

            --y;
            break;
        }
        case 4:{

            break;
        }
        }

推荐答案

++i在增加i的值后返回. i++在递增之前返回i的值.

++i returns the value of i after it has been incremented. i++ returns the value of i before incrementing.

当++出现在其操作数之前时，它称为前递增"运算符，当它出现在其之后时，则称为后递增"运算符.

When the ++ comes before its operand it is called the "pre-increment" operator, and when it comes after it is called the "post-increment" operator.

仅当您对结果进行某些操作时，这种区别才重要.

This distinction is only important if you do something with the result.

var i = 0, j = 0;

alert(++i);  // alerts 1
alert(j++);  // alerts 0

要注意的一件事是，即使i++在递增之前返回该值，但在将其转换为数字后仍会返回该值.

One thing to note though is that even though i++ returns the value before incrementing, it still returns the value after it has been converted to a number.

所以

var s = "1";
alert(typeof s++);  // alerts "number"
alert(s);  // alerts 2, not "11" as if by ("1" + 1)

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