javascript - 映射到另一个并比较节点

Question

我对迭代到 JS 对象和 JavaScript 中的一些数组函数有些怀疑。假设我有这些变量:

var json1 = "[{"id": 1, "name":"x"}, {"id": 2, "name":"y"}]";
var json2 = "[{"id": 1, "name":"x"}, {"id": 2, "name":"y"}, {"id": 3, "name":"z"}]";

如何创建一个仅包含数组中 ID 的变量

var ids1 = json1.ids (would be 1,2)
var ids2 = json2.ids (would be 1,2,3)

然后只用不同的 ID 创建另一个变量

var idsdiff = diff(ids1, ids2) (would be 3)

Answer 1

var json1 = [{"id":1,"name":"x"}, {"id":2,"name":"y"}],
    json2 = [{"id":1,"name":"x"}, {"id":2,"name":"y"}, {"id":3,"name":"z"}],
    result1 = json1.map(function (a) { return a.id; }),
    result2 = json2.map(function (a) { return a.id; });

var diffs = result2.filter(function (item) {	
    return result1.indexOf(item) < 0;
});

console.log(result1);
console.log(result2);
console.log(diffs);

注意 indexOf 和 filter 和 map 在 iE9 之前的 iE 中不可用>.

更新:根据@alexandru-Ionutmihai 的评论，过滤器将在 [1,2,4] 和 [1,2,3]

上失败

这段代码看起来更好:

var json1 = [{"id":1,"name":"x"}, {"id":2,"name":"y"}],
        json2 = [{"id":1,"name":"x"}, {"id":2,"name":"y"}, {"id":3,"name":"z"}],
        result1 = json1.map(function (a) { return a.id; }),
        result2 = json2.map(function (a) { return a.id; });

//as per @alexandru-Ionutmihai this is inaccurate for [1,2,4] and [1,2,3]
/*var diffs = result2.filter(function (item) {	
    return result1.indexOf(item) < 0;
});*/

//here's a workaround
function arr_diff(a, b) {
  var i,
    la = a.length,
    lb = b.length,
    res = [];
  if (!la)
    return b;
  else if (!lb)
    return a;
  for (i = 0; i < la; i++) {
    if (b.indexOf(a[i]) === -1)
      res.push(a[i]);
  }
  for (i = 0; i < lb; i++) {
    if (a.indexOf(b[i]) === -1) res.push(b[i]);
  }
  return res;
}

var diffs = arr_diff(result1, result2),
  testDiff = arr_diff([1, 2, 4], [1, 2, 3]);

console.log(result1);
console.log(result2);
console.log(diffs);
console.log(testDiff);

arr_diff 感谢@Nomaed 对此 question's 的评论回答。