55 lines
1.2 KiB
JavaScript
55 lines
1.2 KiB
JavaScript
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'use strict'
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const ExtendableError = require('es6-error')
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const constants = require('./constants')
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class UnwrapError extends ExtendableError {
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constructor (thenable) {
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super('Could not unwrap asynchronous thenable')
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this.thenable = thenable
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}
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}
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// Logic is derived from the Promise Resolution Procedure, as described in the
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// Promises/A+ specification: https://promisesaplus.com/#point-45
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//
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// Note that there is no cycle detection.
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function unwrapSync (x) {
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if (!x || typeof x !== 'object' && typeof x !== 'function') {
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return x
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}
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const then = x.then
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if (typeof then !== 'function') return x
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let state = constants.PENDING
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let value
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const unwrapValue = y => {
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if (state === constants.PENDING) {
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state = constants.RESOLVED
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value = y
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}
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}
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const unwrapReason = r => {
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if (state === constants.PENDING) {
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state = constants.REJECTED
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value = r
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}
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}
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then.call(x, unwrapValue, unwrapReason)
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if (state === constants.PENDING) {
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state = constants.ASYNC
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throw new UnwrapError(x)
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}
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if (state === constants.RESOLVED) {
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return unwrapSync(value)
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}
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// state === REJECTED
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throw value
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}
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module.exports = unwrapSync
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