How to dynamically add attributes to objects in javascript?

Question

As we all know, we can use if else to add an attribute to object like this:

if(key){
  obj[key] = value
}

but I have a lot of keys.

I know I can get this done like this:

keyValues.forEach(({key,value})=>{
if(key){
  obj[key] = value
}
}

but i want to know can i do this in another way like:

obj={
 [this.key1?'key1':undefined]:this.key1,
 [this.key2?'key2':undefined]:this.key2,
}

in this way,the object will get an attribute which key is undefined... how can i do to remove undefined attribute and keep the code style in the second way.

Elmar Caixeta · Accepted Answer · 2021-03-25 02:38:58Z

1

Using keyValues from post:

let obj = {};
let keyValues = [
    {
        "key": "a",
        "value": 1
    },
    {
        "key": "b",
        "value": 2
    },
    {
        "key": "c",
        "value": 3
    },
    {
        "value": "nothing"
    }
];

/**
* @returns only 'a', 'b' and 'c' keys
*/
Object.assign(obj, keyValues.reduce((acc, { key, value }) => ({
    ...acc,
    ...key ? { [key]: value } : {},
}), {}))

or u can use the _reject from lodash https://lodash.com/docs/4.17.15#reject

Object.assign(obj, _.reject(keyValues, v => !v.key).reduce((acc, { key, value }) => ({
    ...acc,
    [key]: value,
}), {}))

edited Mar 25, 2021 at 2:38

answered Mar 25, 2021 at 2:19

Elmar Caixeta

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Comments

George Neto · Accepted Answer · 2021-03-25 01:53:55Z

0

After mounting your obj, you can use the delete operator from js

delete obj.undefined

this will keep your obj clean, if you insist on instantiating it that way;

answered Mar 25, 2021 at 1:53

George Neto

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Comments

hgb123 · Accepted Answer · 2021-03-25 01:57:15Z

0

You could wrap it in a helper function that remove falsy keys

const omit = (obj) =>
  Object.fromEntries(
    Object.entries(obj).filter(
      ([key]) => !["undefined", "null", "false", ""].includes(key)
    )
  );

const obj = omit({
  [undefined]: 1,
  [false]: 2,
  [null]: 3,
  a: "b",
});

console.log(obj);

answered Mar 25, 2021 at 1:57

hgb123

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