pinafore/routes/_utils/reselect.js

39 lines
1.2 KiB
JavaScript

// Avoid re-renders by caching the most recent value of an array
// or an object, using an approach similar to https://github.com/reactjs/reselect.
// This avoids the issue where Svelte may keep re-rendering because it doesn't
// know if an object/array has changed or not.
import isEqual from 'lodash-es/isEqual'
if (process.browser && process.env.NODE_ENV !== 'production') {
window.reselectStats = {}
}
export function reselect (store, outputKey, inputKey) {
let prevValue
let nextValue
let count = 0
let countKey = `${outputKey}_reselectCount`
store.compute(countKey, [inputKey], input => {
if (process.browser && process.env.NODE_ENV !== 'production') {
window.reselectStats[inputKey] = window.reselectStats[inputKey] || {numInputChanges: 0, numOutputChanges: 0}
window.reselectStats[inputKey].numInputChanges++
}
if (!isEqual(prevValue, input)) {
nextValue = input
count++
}
return count
})
store.compute(outputKey, [countKey], () => {
if (process.browser && process.env.NODE_ENV !== 'production') {
window.reselectStats[inputKey].numOutputChanges++
}
prevValue = nextValue
nextValue = null
return prevValue
})
}