比较两个不同长度的数组，并排除匹配项

Question

I have two JSON arrays:

{"Array1":[ 
  { "_id": "1234"},
  { "_id": "5678"}, 
  { "_id": "3456"} ]}

and

{"Array2":[ 
  { "_id": "1234"},
  { "_id": "5678"} ]}

How do I compare the two in node.js and return only the difference from Array1 ?

I have attempted the following:

if (Array1.every(function (u, i) { return u._id === Array2[i]._id;})) {
    Array1.splice(i, 1);
}

Answer 1

I wouldn't use Array.prototype.every for the task of filtering out the identical _id s, as that is not its intended function.

Instead, I suggest you use the Array.prototype.filter method, along with Array.prototype.map , as shown below:

 const obj1 = {"Array1":[ { "_id": "1234"}, { "_id": "5678"}, { "_id": "3456"} ]}; const obj2 = {"Array2":[ { "_id": "1234"}, { "_id": "5678"} ]}; console.log(obj1.Array1.filter(a1 => obj2.Array2.map(a2 => a2._id).indexOf(a1._id) < 0)); 

ES5:

 var obj1 = {"Array1":[ { "_id": "1234"}, { "_id": "5678"}, { "_id": "3456"} ]}; var obj2 = {"Array2":[ { "_id": "1234"}, { "_id": "5678"} ]}; console.log(obj1.Array1.filter(function (a1) { return obj2.Array2.map(function (a2) { return a2._id; }).indexOf(a1._id) < 0; }));