Caching JavaScript promise results

Question

I would make one call to the server to get a list of items. How do I make sure that only one call is made and the collections is processed only once to create a key value ma

Answer 1

Try npm dedup-async, which caches duplicated promise calls if there's a pending one, so concurrent promise calls trigger only one actual task.

const dedupa = require('dedup-async')

let evil
let n = 0

function task() {
    return new Promise((resolve, reject) => {
        if (evil)
            throw 'Duplicated concurrent call!'
        evil = true

        setTimeout(() => {
            console.log('Working...')
            evil = false
            resolve(n++)
        }, 100)
    })
}

function test() {
    dedupa(task)
        .then (d => console.log('Finish:', d))
        .catch(e => console.log('Error:', e))
}

test()                //Prints 'Working...', resolves 0
test()                //No print,            resolves 0
setTimeout(test, 200) //Prints 'Working...', resolves 1