How to filter array when object key value is in array

You can do it with Array.prototype.filter(),

var data = { records : [{ "empid": 1, "fname": "X", "lname": "Y" }, { "empid": 2, "fname": "A", "lname": "Y" }, { "empid": 3, "fname": "B", "lname": "Y" }, { "empid": 4, "fname": "C", "lname": "Y" }, { "empid": 5, "fname": "C", "lname": "Y" }] }
var empIds = [1,4,5]
var filteredArray = data.records.filter(function(itm){
  return empIds.indexOf(itm.empid) > -1;
});

filteredArray = { records : filteredArray };

If​ the ​callBack​ returns a ​true​ value, then the ​itm​ passed to that particular callBack will be filtered out. You can read more about it here.​​​​​​

This is a fast solution with a temporary object.

var records = [{ "empid": 1, "fname": "X", "lname": "Y" }, { "empid": 2, "fname": "A", "lname": "Y" }, { "empid": 3, "fname": "B", "lname": "Y" }, { "empid": 4, "fname": "C", "lname": "Y" }, { "empid": 5, "fname": "C", "lname": "Y" }],
    empid = [1, 4, 5],
    object = {},
    result;

records.forEach(function (a) {
    object[a.empid] = a;
});

result = empid.map(function (a) {
    return object[a];
});
document.write('<pre>' + JSON.stringify(result, 0, 4) + '</pre>');

You can use Array#filter function and additional array for storing sorted values;

var recordsSorted = []

ids.forEach(function(e) {
    recordsSorted.push(records.filter(function(o) {
        return o.empid === e;
    }));
});

console.log(recordsSorted);

Result:

[ [ { empid: 1, fname: 'X', lname: 'Y' } ],
  [ { empid: 4, fname: 'C', lname: 'Y' } ],
  [ { empid: 5, fname: 'C', lname: 'Y' } ] ]

In 2019 using ES6:

const ids = [1, 4, 5],
  data = {
    records: [{
      "empid": 1,
      "fname": "X",
      "lname": "Y"
    }, {
      "empid": 2,
      "fname": "A",
      "lname": "Y"
    }, {
      "empid": 3,
      "fname": "B",
      "lname": "Y"
    }, {
      "empid": 4,
      "fname": "C",
      "lname": "Y"
    }, {
      "empid": 5,
      "fname": "C",
      "lname": "Y"
    }]
  };


data.records = data.records.filter( i => ids.includes( i.empid ) );

console.info( data );