Using spread syntax to dynamically merge objects

Question

The new spread syntax can be used to elegantly merge several objects in the following way:

const person = { name: 'David Walsh', gender: 'Male' };
const tools = { computer: 'Mac', editor: 'Atom' };

const summary = {...person, ...tools};

Is there a way to use this in a dynamical scenario, where the number and names of the objects to be merged are not known beforehand?

If

var objects_to_be_merged = get_objects();

generated an iterable list of objects during runtime, how can I use the spread operator iteratively to create a summary object like in the example above?

Nenad Vracar · Accepted Answer · 2018-01-24 13:44:58Z

4

You can use Object.assign() with spread syntax to merge array of objects.

const person = { name: 'David Walsh', gender: 'Male' };
const tools = { computer: 'Mac', editor: 'Atom' };

const objects = () => [person, tools];
const summary = Object.assign({}, ...objects());
console.log(summary)

answered Jan 24, 2018 at 13:44

Nenad Vracar

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2 Comments

neaumusic Over a year ago

Worth noting that { ...[] } results in {}

neaumusic Over a year ago

Also, { ...{} } results in {}

T.J. Crowder · Accepted Answer · 2018-01-24 13:44:26Z

2

Is there a way to use this in a dynamical scenario, where the number and names of the objects to be merged are not known beforehand?

Not with property spread notation*, no. Instead, you'd use Object.assign. If the number of objects is unknown, you'd pass it an array using (amusingly) array spread:

const combined = Object.assign({}, ...get_objects());

(Presumably get_objects() returns an array or other iterable.)

* property spread is a Stage 3 proposal at the moment, but it's supported without a runtime flag in current Chrome and Firefox and likely to be in ES2018. (Whereas array spread was in ES2015.)

answered Jan 24, 2018 at 13:44

T.J. Crowder

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