git ssb

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var computed = require('./computed')
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var resolve = require('./resolve')
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var isObservable = require('./is-observable')
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module.exports = Merge
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function Merge (sources) {
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  var raw = {}
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  var value = {}
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  var keys = new Set()
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  var instance = computed.extended(sources, function update () {
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    var currentKeys = []
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    forEach(sources, function (source) {
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      forEachPair(source, function (key, rawValue) {
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        currentKeys.push(key)
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        keys.add(key)
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        raw[key] = rawValue
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        value[key] = resolve(rawValue)
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      })
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    })
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    // remove deleted keys
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    Array.from(keys.values()).filter(function (k) {
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      return !currentKeys.includes(k)
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    }).forEach(function (key) {
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      keys.delete(key)
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      delete raw[key]
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      delete value[key]
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    })
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    return value
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  })
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  var result = function MutantMerge (listener) {
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    return instance(listener)
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  }
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  result.keys = function () {
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    instance.checkUpdated()
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    return Array.from(keys.values())
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  }
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  result.get = function (key) {
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    instance.checkUpdated()
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    return raw[key]
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  }
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  return result
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}
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function forEach (sources, fn) {
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  if (sources && !sources.forEach) {
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    sources = resolve(sources)
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  }
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  if (sources && sources.forEach) {
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    sources.forEach(fn)
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  }
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}
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function forEachPair (source, fn) {
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  if (source) {
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    if (isObservable(source) && source.keys && source.get) {
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      resolve(source.keys).forEach(function (key) {
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        fn(key, source.get(key))
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      })
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    }
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  }
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}
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