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55 lines
1.4 KiB
JavaScript
55 lines
1.4 KiB
JavaScript
6 years ago
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/*
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usage:
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// do something to a list of things
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asyncMap(myListOfStuff, function (thing, cb) { doSomething(thing.foo, cb) }, cb)
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// do more than one thing to each item
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asyncMap(list, fooFn, barFn, cb)
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*/
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module.exports = asyncMap
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function asyncMap () {
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var steps = Array.prototype.slice.call(arguments)
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, list = steps.shift() || []
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, cb_ = steps.pop()
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if (typeof cb_ !== "function") throw new Error(
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"No callback provided to asyncMap")
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if (!list) return cb_(null, [])
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if (!Array.isArray(list)) list = [list]
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var n = steps.length
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, data = [] // 2d array
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, errState = null
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, l = list.length
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, a = l * n
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if (!a) return cb_(null, [])
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function cb (er) {
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if (er && !errState) errState = er
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var argLen = arguments.length
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for (var i = 1; i < argLen; i ++) if (arguments[i] !== undefined) {
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data[i - 1] = (data[i - 1] || []).concat(arguments[i])
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}
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// see if any new things have been added.
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if (list.length > l) {
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var newList = list.slice(l)
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a += (list.length - l) * n
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l = list.length
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process.nextTick(function () {
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newList.forEach(function (ar) {
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steps.forEach(function (fn) { fn(ar, cb) })
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})
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})
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}
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if (--a === 0) cb_.apply(null, [errState].concat(data))
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}
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// expect the supplied cb function to be called
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// "n" times for each thing in the array.
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list.forEach(function (ar) {
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steps.forEach(function (fn) { fn(ar, cb) })
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})
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}
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