Implementing various set methods for objects

Question

I am looking to compare keys in two objects. Is there a built-in method to do this or a shorter version of something like the following?

// treat keys as enumerableOwn
// 1. Difference: {}.keys() - {}.keys()
Object.prototype.diff = function(obj2) {
    let thisKeys = Object.keys(this);
    let arr = [];
    for (let i=0; i < thisKeys.length; i++) {
        let key = thisKeys[i];
        if (!(obj2.hasOwnProperty(key))) {
            arr.push(key);
        }
    }
    return arr;
}
// 2. Intersection: {}.keys() && {}.keys()
Object.prototype.same = function(obj2) {
    let thisKeys = Object.keys(this);
    let arr = [];
    for (let i=0; i < thisKeys.length; i++) {
        let key = thisKeys[i];
        if (obj2.hasOwnProperty(key)) {
            arr.push(key);
        }
    }
    return arr;
}
// 3. Union: {}.keys() || {}.keys()
Object.prototype.union = function(obj2) {
    let arr = Object.keys(this);
    for (let key of Object.keys(obj2)) {
        if (!(obj1.hasOwnProperty(key))) {
            arr.push(key);
        }
    }
    return arr;
}


let obj1 = {x: 1, y: 2};
let obj2 = {x: 3, z: 4}
console.log(obj1.diff(obj2));
console.log(obj1.same(obj2));
console.log(obj1.union(obj2));

First of all, don't put methods on Object.prototype like that or even at all! — Bergi
– Bergi, Commented Mar 18, 2022 at 17:39
Since you're diffing/intersecting/combining only lists of strings, not the objects themselves, you probably should not make these methods of Object. And for array intersection etc, yes there are shorter ways to do it — Bergi
– Bergi, Commented Mar 18, 2022 at 17:42
@Bergi so instead should it use normal functions or make a class that inherits the Object type? — David542
– David542, Commented Mar 18, 2022 at 17:54

David542 · Accepted Answer · 2022-03-18 17:53:37Z

1

A slightly different and shorter way to do it would be as follows:

function diff(obj1, obj2) {
    let keys = Object.keys(obj2);
    return Object.keys(obj1).filter((elem) => !keys.includes(elem))
};
function same(obj1, obj2) {
    let keys = Object.keys(obj2);
    return Object.keys(obj1).filter((elem) => keys.includes(elem));
}
function union(obj1, obj2) {
    let keys = [...Object.keys(obj1), ...Object.keys(obj2)];
    return Array.from(new Set(keys));
}

let obj1 = {x: 1, y: 2};
let obj2 = {x: 3, z: 4}
console.log(diff(obj1, obj2));
console.log(same(obj1, obj2));
console.log(union(obj1, obj2));

answered Mar 18, 2022 at 17:53

David542

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