+ =(加上相等)如何工作？

Question

我对+ =符号有点困惑.它是如何工作的？

1. 1 += 2 // 等于 ？

2. 还有这个

   var data = [1,2,3,4,5];
   var sum = 0;
   data.forEach(function(value) {
       sum += value; 
   });
   sum = ?
   

Answer 1

1 += 2 是语法错误(左侧必须是变量).

x += y是简写x = x + y.

Answer 2

1)1 + = 2 //等于？

这在语法上是无效的.左侧必须是变量.例如.

var mynum = 1;
mynum += 2;
// now mynum is 3.

mynum += 2; 只是一个简短的形式 mynum = mynum + 2;

2)

var data = [1,2,3,4,5];
var sum = 0;
data.forEach(function(value) {
    sum += value; 
});

Sum现在是15.展开forEach我们有:

var sum = 0;
sum += 1; // sum is 1
sum += 2; // sum is 3
sum += 3; // sum is 6
sum += 4; // sum is 10
sum += 5; // sum is 15

Answer 3

这只是一个简短形式:

sum = sum + value;

Answer 4

+=在JavaScript(以及许多其他语言)中,将右侧添加到左侧的变量,将结果存储在该变量中.1 +=2因此,你的例子没有意义.这是一个例子:

var x = 5;
x += 4; // x now equals 9, same as writing x = x + 4;
x -= 3; // x now equals 6, same as writing x = x - 3;
x *= 2; // x now equals 12, same as writing x = x * 2;
x /= 3; // x now equals 4, same as writing x = x / 3;

在您的具体示例中,循环是对数组中的数字求和data.

Answer 5

+= operator用于连接字符串或添加数字.

它将使用旁边的金额增加sum变量.

var sum = 0;
var valueAdded = 5; 

sum += valueAdded;

sum = 5