git ssb

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var watch = require('mutant/watch')
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var computed = require('mutant/computed')
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var Value = require('mutant/value')
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module.exports = Sustained
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// only broadcast value changes once a truthy value has stayed constant for more than timeThreshold
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function Sustained (obs, timeThreshold, checkUpdateImmediately) {
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  var outputValue = Value(obs())
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  var lastValue = null
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  var timer = null
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  return computed(outputValue, v => v, {
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    onListen: () => watch(obs, onChange)
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  })
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  function onChange (value) {
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    if (checkUpdateImmediately && checkUpdateImmediately(value)) { // update immediately for falsy values
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      clearTimeout(timer)
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      update()
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    } else if (value !== lastValue) {
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      clearTimeout(timer)
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      timer = setTimeout(update, timeThreshold)
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    }
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    lastValue = value
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  }
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  function update () {
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    var value = obs()
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    if (value !== outputValue()) {
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      outputValue.set(value)
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    }
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  }
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}
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