JavaScript -- search for array values in object

Question

I have an array and an array of objects. I want to search each value in the array in the array of objects and if it doesnt exist, I want to remove the value from the array.

var arr= [1,2,3,4];
var recs = [{id:1},{id:2},{id:3}]; //4 doesnt exist in recs, remove from arr
//arr = [1,2,3];

Heres my attempt. Obviously does not work. I am not sure how I can compare each arr index with all the values in recs before moving on the next arr index:

var arr= [1, 2, 3, 4], index;
var recs = [{a:1},{a:2},{a:3}];
for(var i = 0; i<arr.length; i++){
 for(var val in recs[i]){
 if(arr[i] != recs[i][val]){
 index = arr.indexOf(arr[i]);
 arr.splice(index, 1); 
 }
 }
}

thank you!!

• abc123: Possible duplicate of Find object by id in array of javascript objects
• Katana314: @abc123 I think the question has more to do with looping through an array and removing elements (the hard part) than it does to do with finding objects.
• jcaron: @Katana314 the code in the question has so many issues it's hard to say what the main issue is :-)
• abc123: @Katana314 answer two on the above literally shows how to go through an create the array that he wants...removing would be 1 extra step.

Answer 1

If you are okay with leaving your original array instance alone and creating a new one (essentially treating it as immutable)

var newArr = arr.filter(function(num) {
 return !recs.every(function(obj) {
 return obj.a !== num;
 });
});

Detail of the methods used: Array.filter is passed a function, runs that function on each element inside, and then returns a new array with only the elements that returned true in the function.

Array.every works a little similar, but returns a Boolean, true or false. It returns true if all of the elements of the array returned true inside of the function.

Answer 2

var arr= [1, 2, 3, 4];
var recs = [{a:1},{a:2},{a:3}];
// don't use var in for loops.
// Variables declared with var have function scope, so declare them at the top of your function
var i;
var j;
var value;
var found;
// iterate over the array
for (i = 0; i < arr.length; i++)
{
 value = arr[i];
 found = false;
 // iterate over the other array
 for (j = 0 ; j < recs.length ; j++)
 {
 // if we found what we were looking for, make a note and exit loop
 if (recs[j].a == value)
 {
 found = true;
 break;
 }
 }
 if (!found)
 {
 arr.splice(i, 1);
 // To compensate the loop's i++, to avoid skipping the next entry
 i--;
 }
}
alert(arr.join(','));