Javascript object generator

Question

Is there a generator approach to constructing a mapping (object)? I just need key/value mapping.

For generating array, I can write something like this

function* rangeA(start, stop) {
  while(start < stop)
    yield start++
}

let data = [...rangeA(1, 3), ...rangeA(20, 22)]
// data is [1, 2, 20, 21]

Non generator approach to construct an object in a similar way can look like this

function rangeB(start, stop) {
  let result = {}
  while(start < stop) {
    result[start] = start
    start++
  }
  return result
}
let data = {...rangeB(1, 3), ...rangeB(20, 22)}
// data is {1: 1, 2: 2, 20: 20, 21: 21}

Is there a generator approach to construct an object? Something like this

// DOES NOT WORK
function* rangeC(start, stop) {
  while(start < stop) {
    yield {[start]: start}
    start++
  }
}
let data = {...rangeC(1, 3), ...rangeC(20, 22)}
// data is unfortunately an empty object

let data2 = [...rangeC(1, 3), ...rangeC(20, 22)]
// data2 is obviously [{1: 1}, {2: 2}, {3: 3}, {20: 20}, {21: 21}]
// which is not what I want.

let data3 = data2.reduce((a, b) => ({...a, ...b}))
// data3 is finally {1: 1, 2: 2, 20: 20, 21: 21}
// but it seems overcomplicated to me

Why is using a generator important? The rangeC() function could be written as a simple function. — Pointy
– Pointy, Commented Jul 7, 2022 at 12:01
@Pointy I'm coming from other languages where this is possible, so I need to know how to do this in JavaScript. I already know of a solution using a simple rangeB function. If that's not what you have in mind, then please just advise/direct me where to look. Maybe it's just a bad idea to use generators for this. — j123b567
– j123b567, Commented Jul 7, 2022 at 12:14
I don't think it's a bad idea or anything, I was just curious about the motivation or some particular problem you are trying to solve. — Pointy
– Pointy, Commented Jul 7, 2022 at 14:54

j123b567 · Accepted Answer · 2022-07-07 12:17:18Z

2

Try using Object.fromEntries:

function* rangeC(start, stop) {
  while(start < stop) {
    // Replace the curly brackets with square ones here
    yield [start, start]
    start++
  }
}
let data = Object.fromEntries([...rangeC(1, 3), ...rangeC(20, 22)])

For one generator, you can pass it directly:

let data = Object.fromEntries(range(1,3))

Or create a chain method to process multiple:

function* chain(...generators) {
    for (let generator of generators) {
        yield* generator;
    }
}

let data = Object.fromEntries(chain(rangeC(1,3), rangeC(10,15)))

edited Jul 7, 2022 at 12:17

j123b567

3,4871 gold badge27 silver badges35 bronze badges

answered Jul 7, 2022 at 12:02

mousetail

8,1696 gold badges31 silver badges53 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Javascript object generator

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related