What is the best way to projecting fields of JavaScript object?

Question

I have to project some fields of javascript to new object.

for example I have a below object

var obj = { fn : 'Abc', 
            ln : 'Xyz', 
            id : 123, 
            nt : 'Note', 
            sl : 50000}

and i want new object containing fn and id

var projectedObj = { fn : 'Abc', id : 123 }

on the basis of projection

var projection = { fn : 1, id : 1 }

something like this

var projectedObj = project(obj, projection);

So what is the best way or optimized way to do this.

Answer 1

Just loop through the projection object and get the keys projected. For example,

function project(obj, projection) {
    let projectedObj = {}
    for(let key in projection) {
        projectedObj[key] = obj[key];
    }
    return projectedObj;
}

Answer 2

You can use array#reduce and iterate through all the keys of projection object and based on the key extract the values from the original object and create your new object.

var project = (o, p) => {
  return Object.keys(p).reduce((r,k) => {
    r[k] = o[k] || '';
    return r;
  },{});
}

var obj = { fn : 'Abc', ln : 'Xyz', id : 123,  nt : 'Note', sl : 50000};
var projection = { fn : 1, id : 1 };
var projectedObj = project(obj, projection);
console.log(projectedObj);

You can also use array#map with Object#assign to create your new object.

var project = (o, p) => {
  return Object.assign(...Object.keys(p).map(k => ({[k]: o[k]})));
}

var obj = { fn : 'Abc', ln : 'Xyz', id : 123,  nt : 'Note', sl : 50000};
var projection = { fn : 1, id : 1 };
var projectedObj = project(obj, projection);
console.log(projectedObj);