87 lines
2.2 KiB
JavaScript
87 lines
2.2 KiB
JavaScript
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/**
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* Cancel token
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* @private
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* @type { Symbol }
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*/
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const CANCEL = Symbol()
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/**
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* Helper that can be returned by ruit function to cancel the tasks chain
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* @returns { Symbol } internal private constant
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* @example
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*
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* ruit(
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* 100,
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* num => Math.random() * num
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* num => num > 50 ? ruit.cancel() : num
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* num => num - 2
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* ).then(result => {
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* console.log(result) // here we will get only number lower than 50
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* })
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*
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*/
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ruit.cancel = () => CANCEL
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/**
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* The same as ruit() but with the arguments inverted from right to left
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* @param { * } tasks - list of tasks to process sequentially
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* @returns { Promise } a promise containing the result of the whole chain
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* @example
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*
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* const curry = f => a => b => f(a, b)
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* const add = (a, b) => a + b
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*
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* const addOne = curry(add)(1)
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*
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* const squareAsync = (num) => {
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* return new Promise(r => {
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* setTimeout(r, 500, num * 2)
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* })
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* }
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*
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* // a -> a + a -> a * 2
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* // basically from right to left: 1 => 1 + 1 => 2 * 2
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* ruit.compose(squareAsync, addOne, 1).then(result => console.log(result)) // 4
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*/
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ruit.compose = (...tasks) => ruit(...tasks.reverse())
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/**
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* Serialize a list of sync and async tasks from left to right
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* @param { * } tasks - list of tasks to process sequentially
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* @returns { Promise } a promise containing the result of the whole chain
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* @example
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*
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* const curry = f => a => b => f(a, b)
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* const add = (a, b) => a + b
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*
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* const addOne = curry(add)(1)
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*
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* const squareAsync = (num) => {
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* return new Promise(r => {
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* setTimeout(r, 500, num * 2)
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* })
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* }
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*
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* // a -> a + a -> a * 2
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* // basically from left to right: 1 => 1 + 1 => 2 * 2
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* ruit(1, addOne, squareAsync).then(result => console.log(result)) // 4
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*/
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export default function ruit(...tasks) {
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return new Promise((resolve, reject) => {
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return (function run(queue, result) {
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if (!queue.length) return resolve(result)
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const [task, ...rest] = queue
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const value = typeof task === 'function' ? task(result) : task
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const done = v => run(rest, v)
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// check against nil values
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if (value != null) {
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if (value === CANCEL) return
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if (value.then) return value.then(done, reject)
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}
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return Promise.resolve(done(value))
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})(tasks)
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})
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}
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