如何在forEach循环中分配值？

Question

我预计第一个console.log为[0,10,20,30]，第二个为[0,100,20,30]：

＆＃13;

＆＃13;

var arr = [0,10,20,30]
console.log(arr)
arr.forEach(each)
console.log(arr)

function each(data,index) {
   if (index === 1) {
      data = 100 // This isn't assigned to arr[1]
   }
}

＆＃13;

＆＃13;

＆＃13;

Answer 1

您正在为本地变量分配值。要分配给实际索引，需要数组和索引，Array#forEach的回调API的参数二和三

＆＃13;

＆＃13;

var arr = [0,10,20,30]
console.log(arr)
arr.forEach(each)
console.log(arr)

function each(data,index, array) {
   if (index === 1) {
      array[index] = 100;
   }
}

＆＃13;

.as-console-wrapper { max-height: 100% !important; top: 0; }

＆＃13;

＆＃13;

＆＃13;