python dict.update() equivalent in javascript

Question

I want to update the dictionary in javascript- modify the existing values or add new values- same as python dictionary update.

dict+ or dict.update() seem not be working. Is it possible to do so in javascript?

Thanks in advance!

data={"abc":{1:2,3:4}}

if (key in d) {
            d[key].update(data[key]);
        }
        else {
            d[key]={};
            d[key]=data[key];
        }

EDIT: The updating dictionary is working fine as follow-

dg={"abc":{1:2,3:4},"sdc":{1:2,4:5}}
function upd(data) {
    for (key in data) {
        if (key in dg) {
            for (key2 in data[key]) {
                dg[key][key2]=data[key][key2];
            }
        }
        else {
            dg[key]={};
            for (key2 in data[key]) {
                dg[key][key2]=data[key][key2];
            }
        }

but if i try separating the function as-

var old={};
var new={};
function update_dict(old,new) {
console.log(new,old);
    for (key2 in new) {
                old[key2]=new[key2];
            }
    return old;
}
function upd(data) {
for (key in data) {
    if (key in dg) {
        dg[key]=update_dict(dg[key],data[key]);
    }
    else {
        dg[key]={};
        dg[key]=update_dict(dg[key],data[key]);
    }

It is throwing an error saying Uncaught SyntaxError: Unexpected token new. I have really tried a lot of permutations, please suggest. Thanks a lot!

Answer 1

You can use the destructuring assignment.

const first_dict = { 'key_one': 'value_one', 'key_two': 'value_two' } 
const second_dict = { 'key_one': 'value_from_second_dict', 'key_three': 'value_three' }

const accumulative = {
  ...first_dict,
  ...second_dict
}

console.log(accumulative)

/* 
[object Object] {
  key_one: "value_from_second_dict",
  key_three: "value_three",
  key_two: "value_two"
}
*/

Answer 2

You can use Object.assign() to get the job done. It will create a new object with all the keys updated as well as add any new key value pairs to the newly created object.

const target = {c: 4, d: 5}
const source = {a: 1, b: 2, c: 3};

const newObj = Object.assign({}, target, source);

console.log(newObj); //=> {a: 1, b: 2, c: 3, d: 5}

Note that Object.assign() modifies the first argument which is why we're passing an empty object above.

You can even pass in a sequence of objects to update the target object, check out the MDN link for more info