javascript - 如何获取两个数组对象之间的差异项？

Question

这里我有两个数组，但它们不是简单的数组。见下文:

var a = [{"id":1,"in":1,"num":3000},{"id":2,"in":1,"num":1500},{"id":3,"in":1,"num":1000}]
var b = [{"id":1,"in":0,"num":1000},{"id":2,"in":0,"num":1000}]

for (var i = a.length - 1; i >= 0; i--) {
     for (var j =b.length - 1; j >= 0; j--) {
        if( a[i]['id'] == b[j]['id']){
             a[i]['rest'] = a[i]['num'] - b[j]['num']
         }
      }
 }
 console.log(a)

但我无法获取 id 3，因为 id 3 不在 b 数组中。请帮忙。

这就是我想要的答案

a = [
   {"id":1,"in":1,"num":3000,"rest":2000},
   {"id":2,"in":1,"num":1500,"rest":500},
   {"id":3,"in":1,"num":1000,"rest":1000}
]

谢谢

Answer 1

所以您想从 a 中的相应“num”中减去 b 中的“num”，以获取 a 的每个元素？不仅仅是迭代 a 并检查它是否也包含在 b 中:

var a = [{"id":1,"in":1,"num":3000},{"id":2,"in":1,"num":1500},{"id":3,"in":1,"num":1000}]
var b = [{"id":1,"in":0,"num":1000},{"id":2,"in":0,"num":1000}]

for (var i = a.length - 1; i >= 0; i--) {
  a[i]['rest'] = a[i]['num'];
  for (var j =b.length - 1; j >= 0; j--) {
    if( a[i]['id'] == b[j]['id']){
     a[i]['rest'] = a[i]['num'] - b[j]['num'];
     break;
    }
  }
}