How to compare the contents of two JSON files with TypeScript?

Question

How can I compare the contents of two JSON files in Angular and achieve the following result:

Let's say that I have a default.json file that looks like this:

default.json

 {
  "name": "John"
  "age": 30,
  "car1": "Ford"
  "car2": "BMW"
  "car3": "Fiat"
 }

And another specific.json file that looks like this:

specific.json

 {
  "name": "Doe",
  "car1": "Tesla",
  "car4": "Mercedes"
 }

The default.json contains always all possible keys and the specific.json the keys, which should be overwritten and additional keys, which are not contained in the default.json (in my example: "car4").

Now the following should be checked by the comparison:

If a specific key (in my example "name" and "car1") has a different value in the specific.json than in the default.json for the same keys, then these values should be overwritten and used. Otherwise always the default values from the default.json and the additional values from the specific.json of course (in my example "car4").

At the end both files should be used, so the specific.json serves only as an update or extension of the default.json. I need this functionality in an Angular app, where I have to compare two JSON files and then use the ngx-translate library to provide specific translations based on specific business cases of the application. Check also my question about this topic please if you want: Translations based on specific keys in custom JSON files and business cases with ngx-translate (Angular 7)

I hope I could explain it well :)

`Object.assign(parsedDatafromDefault, parsedDataFromSpecific)`? — adiga, Feb 26 '19 at 20:26
@tic Because I need it in an Angular app, where I have to compare two JSON files and then use the ngx-translate library to provide specific translations based on specific business cases of the application. — Codehan25, Feb 26 '19 at 20:29
@adiga With this, the equal keys will be overwritten but what about the additional keys that are not in the default.json but in the specific.json? — Codehan25, Feb 26 '19 at 20:35
Then the `specific` property will be taken: [Object.assign()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign) — adiga, Feb 26 '19 at 20:36
Possible duplicate of [How can I get a list of the differences between two JavaScript object graphs?](https://stackoverflow.com/questions/264430/how-can-i-get-a-list-of-the-differences-between-two-javascript-object-graphs) — Heretic Monkey, Feb 26 '19 at 20:37
Possible duplicate of [How can I merge properties of two JavaScript objects dynamically?](https://stackoverflow.com/questions/171251/how-can-i-merge-properties-of-two-javascript-objects-dynamically) — adiga, Feb 26 '19 at 20:37
@tic I did not know that the spread operator overrides the same keys. I'll try that. — Codehan25, Feb 26 '19 at 20:40
@RomanticElectron That will never enter the body of the if, since the condition will always be false. — Heretic Monkey, Feb 26 '19 at 20:41

score 1 · Answer 1 · edited Feb 26 '19 at 20:40

This is not related with Angular, but with JS.

Below example how to do it with objects.

let def = {
  "name": "John",
  "age": 30,
  "car1": "Ford",
  "car2": "BMW",
  "car3": "Fiat"
};

let specific = {
  "name": "Doe",
  "car1": "Tesla",
  "car4": "Mercedes"
}

function compose(def, spec) {
  return Object.assign(def, spec);
}

console.log(compose(def, specific));

Output:

/*
{ 
  name: 'Doe',
  age: 30,
  car1: 'Tesla',
  car2: 'BMW',
  car3: 'Fiat',
  car4: 'Mercedes' 
}
*/

score 1 · Accepted Answer · answered Feb 26 '19 at 21:15

1

Use es6 spread operator to merge (And override) objects

const defaultObj = {
  name: 'John',
  age: 30,
  car1: 'Ford',
  car2: 'BMW',
  car3: 'Fiat'
};

const specificObj = {
  name: 'Doe',
  car1: 'Tesla',
  car4: 'Mercedes'
}

console.log({ ...defaultObj, ...specificObj });

answered Feb 26 '19 at 21:15

tic

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I just tried it and it also seems to work with my ngx-translate solution. I will try to continue working with this solution. Thank you! – Codehan25 Feb 26 '19 at 21:24

How to compare the contents of two JSON files with TypeScript?

2 Answers2