使用 ramda.js assocPath 为多个键分配特定值？

Question

I am quite new to JS and ramda.js. Let's say i have an object consisting of empty objects like this:

obj = { 1: { }, 2: { }, 3: { } }

and array consisting of chosen keys of the obj .

arr = ['1', '2']

What i need is to create a certain key-value pair, for example a: 'value' , inside of the key objects chosen via arr , so the result would look like this:

obj = { 
 1: { a: 'value' }, 
 2: { }, 
 3: { a: 'value' } 
}

I have tried to.map through the keys with

arr.map(key => assocPath([key, 'a'], 'value', obj) )

, and also tried a way with arr.forEach() , but it doesn't work and i believe i may be missing some basic knowledge? Or is there an alternative ramda.js function i should use?

Answer 1

You should be able to do this with .forEach() :

arr.forEach(key => obj[key] = { a: 'value' });

The .map() function is for creating a new array from the elements of a source array, and you don't need to do that.

Answer 2

Take a look at my solution

 const object = { 1: { }, 2: { }, 3: { } } const array = ['1', '3'] function magic(obj, arr) { return arr.reduce((acc, key) => ({...acc, [key]: { a: 'value' }, }), obj) } console.log(magic(object, array))

This is also can be achieved with ramda's functions

 const object = { 1: { }, 2: { }, 3: { } } const array = ['1', '3'] const magicR = R.reduce((acc, key) => R.assocPath([ key, 'a' ], 'value', acc)) console.log(magicR(object, array))

 <script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.26.1/ramda.min.js"></script>

Answer 3

Ramda methods are immutable - they don't mutate the original object, but return a new one. The R.assocPath method is no different in this regard. To update the object, you'll need to iterate the array with R.reduce, use R.assocPath, get a new object, etc...

 const { reduce, assocPath } = R const fn = reduce((o, key) => assocPath([key, 'a'], 'value', o)) const obj = { 1: { }, 2: { }, 3: { } } const arr = ['1', '2'] const result = fn(obj)(arr) console.log(result)

 <script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.26.1/ramda.js"></script>