copy array of objects from another array javascript by comparing elements code example

Example 1: javascript compare object arrays keep only entries not in both

var result = result1.filter(function (o1) {
    return result2.some(function (o2) {
        return o1.id === o2.id; // return the ones with equal id
   });
});
// if you want to be more clever to find those in common:
let result = result1.filter(o1 => result2.some(o2 => o1.id === o2.id));

// To find those in 1 NOT in 2:
let result = result1.filter(o1 => !result2.some(o2 => o1.id === o2.id));

Example 2: match ids from 2 arrays in javascript asynchronous programming

var result1 = [
    {id:1, name:'Sandra', type:'user', username:'sandra'},
    {id:2, name:'John', type:'admin', username:'johnny2'},
    {id:3, name:'Peter', type:'user', username:'pete'},
    {id:4, name:'Bobby', type:'user', username:'be_bob'}
];

var result2 = [
    {id:2, name:'John', email:'[email protected]'},
    {id:4, name:'Bobby', email:'[email protected]'}
];

var props = ['id', 'name'];

var result = result1.filter(function(o1){
    // filter out (!) items in result2
    return !result2.some(function(o2){
        return o1.id === o2.id;          // assumes unique id
    });
}).map(function(o){
    // use reduce to make objects with only the required properties
    // and map to apply this to the filtered array as a whole
    return props.reduce(function(newo, name){
        newo[name] = o[name];
        return newo;
    }, {});
});

document.body.innerHTML = '<pre>' + JSON.stringify(result, null, 4) +
        '</pre>';