Object assign extend immutable array of object

Question

I want to have a immutable original array of object and extend a new one, but seems the code below did nto produce the right result. obj3 became an object instead of an array of object. I even tried lodash's extend.

var obj1 = [{
  abc: 'abc value'
}, {
  def: 'def value'
}];

var obj2 = {
  def: 'new def value'
};

/*var obj3 = _.extend({}, obj1, obj2);
console.log(obj3)
*/

var obj3 = Object.assign({},obj1,obj2);

https://jsbin.com/bawadeqicu/edit?html,js,output

My desire output is

obj1: [{"abc":"abc value"},{"def":"def value"}] // immutable
obj3: [{"abc":"abc value"},{"def":"new def value"}]

Clone the array and assign obj2 as the second element of the new copy. There is no "pretty" way to do this. var obj3 = obj1.slice(); obj3[1] = obj2;. I mean, you could do var obj3 = Object.assign([], obj1, {1: obj2}); but that seems more magic ¯\_(ツ)_/¯ — Felix Kling
– Felix Kling, Commented Jan 6, 2017 at 23:35
check this link github.com/rtfeldman/seamless-immutable/issues/43 — Amr Ashraf
– Amr Ashraf, Commented Jan 7, 2017 at 0:02
Why is the second object updated? Because it has a property def? Do you want to match/merge objects based on property? What should happen if the property name was different? would obj2 simply be added to the array? Would the objects be merged in a different? What if both objects in the array had the same property? What if they have other properties as well? You haven't actually described what the merge rules are so any answer you get will just be an interpretation based on the specific input and output you provided. — Felix Kling
– Felix Kling, Commented Jan 7, 2017 at 0:53

Amr Ashraf · Accepted Answer · 2017-01-06 23:51:01Z

2

Going immutable

Instead of passing the object and mutating it, we will be better off creating a completely new object:

const person = {
  name: 'John',
  age: 28
}
const newPerson = Object.assign({}, person, {
  age: 30
})
console.log(newPerson === person) // false
console.log(person) // { name: 'John', age: 28 }
console.log(newPerson) // { name: 'John', age: 30 }

source

edited Jan 6, 2017 at 23:51

answered Jan 6, 2017 at 23:47

Amr Ashraf

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3 Comments

Jacob Over a year ago

You should elaborate on this; link-only answers are frowned on here since the link may not survive the passage of time.

Amr Ashraf Over a year ago

@Jacob you mean i should write the answer and refer to the link too ??

Elken Chen Over a year ago

I want array of object,not just object.

guest271314 · Accepted Answer · 2017-05-14 00:44:18Z

2

You can use Object.entries(), .map() spread element at obj1 parameter passed to Object.assign() to spread the object elements of obj1 array to the new array.

var obj1 = [{
  abc: 'abc value'
}, {
  def: 'def value'
}];

var obj2 = {
  def: 'new def value'
};

var obj3 = Object.entries(Object.assign({},...obj1, obj2))
           .map(([prop, value]) => ({[prop]:value}));

console.log(
  `obj1:${JSON.stringify(obj1)}`
  , `\nobj2:${JSON.stringify(obj2)}`
  , `\nobj3:${JSON.stringify(obj3)}`
)

edited May 14, 2017 at 0:44

answered Jan 6, 2017 at 23:44

guest271314

1

10 Comments

maioman Over a year ago

this is possibly the correct answer, you need to split the keys into distinct objects,

Felix Kling Over a year ago

This will fail if the objects have the same property name.

guest271314 Over a year ago

@FelixKling Can you describe what you mean?

Felix Kling Over a year ago

If all objects had the property abc, not def, then your code would result in an array with a single object. Of course that might be the expected result, I don't know.

Elken Chen Over a year ago

confusion, i think i rather don't do inmmutable here, just use push() to a new var.

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