JSFiddle - React, Tailwind, and code Playground

by jfriend00

CSS

body {font-family: "Courier New"; font-size: 14px;}

JavaScript

function findUniques(testItems, baseItems) {
    var index = {}, i;
    var result = [];

    // put a1 id values into the index
    for (i = 0; i < baseItems.length; i++) {
        index[baseItems[i].ID] = true;
    }

    // now go through a2 and collect the items in it that are not in the index
    for (i = 0; i < a2.length; i++) {
        if (!(testItems[i].ID in index)) {
            result.push(testItems[i]);
        }
    }
    return(result);
}

var a1 = [ { ID: 2, N:0 }, { ID: 1, N:0 } ];
var a2 = [ { ID: 1, N:0 }, { ID: 2, N:0 }, { ID: 3, N:0 } ];

var result = findUniques(a2, a1);
document.body.innerHTML = JSON.stringify(result);