git ssb

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var isObservable = require('../is-observable')
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var Set = require('../set')
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var watch = require('../watch')
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var caches = new global.WeakMap()
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module.exports = applyProperties
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function applyProperties (target, properties) {
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  var data = caches.get(target)
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  if (!data) {
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    data = { releases: [] }
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    caches.set(target, data)
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  }
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  var classList = Set()
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  if (target.className) {
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    classList.add(target.className)
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  }
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  for (var key in properties) {
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    var valueOrObs = properties[key]
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    var value = resolve(valueOrObs)
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    if (key === 'style') {
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      // TODO: handle observable at root for style objects
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      for (var k in value) {
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        var styleValue = resolve(value[k])
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        var styleObs = isObservable(value[k]) ? value[k] : null
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        target.style.setProperty(k, styleValue)
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        if (styleObs) {
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          data.releases.push(bindStyle(target, styleObs, k))
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        }
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      }
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    } else if (key === 'hooks') {
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      value.forEach(function (v) {
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        var release = v(target)
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        if (typeof release === 'function') {
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          data.releases.push(release)
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        }
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      })
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    } else if (key === 'attributes') {
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      for (var k in value) {
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        var attrValue = resolve(value[k])
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        var attrObs = isObservable(value[k]) ? value[k] : null
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        target.setAttribute(k, attrValue)
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        if (attrObs) {
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          data.releases.push(bindAttr(target, attrObs, k))
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        }
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      }
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    } else if (key === 'events') {
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      for (var name in value) {
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        target.addEventListener(name, value[name], false)
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      }
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    } else if (key.slice(0, 3) === 'ev-') {
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      target.addEventListener(key.slice(3), value, false)
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    } else if (key === 'className' || key === 'classList') {
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      if (Array.isArray(valueOrObs)) {
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        valueOrObs.forEach(function (v) {
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          classList.add(v)
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        })
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      } else {
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        classList.add(valueOrObs)
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      }
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    } else {
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      target[key] = value
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      var obs = isObservable(valueOrObs) ? valueOrObs : null
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      if (obs) {
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        data.releases.push(bind(target, obs, key))
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      }
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    }
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  }
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  watch(classList, function (value) {
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    value = [].concat.apply([], value).filter(present).join(' ')
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    if (value || target.className) {
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      target.className = value
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    }
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  })
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}
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applyProperties.destroy = function (target) {
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  var data = caches.get(target)
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  if (data) {
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    while (data.releases.length) {
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      data.releases.pop()()
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    }
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    caches.delete(target)
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  }
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}
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function bindStyle (target, styleObs, key) {
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  return styleObs(function (value) {
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    target.style.setProperty(key, value)
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  })
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}
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function bindAttr (target, attrObs, key) {
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  return attrObs(function (value) {
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    if (value == null) {
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      target.removeAttribute(key)
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    } else {
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      target.setAttribute(key, value)
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    }
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  })
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}
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function bind (target, obs, key) {
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  return obs(function (toValue) {
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    var fromValue = target.getAttribute(key)
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    if (fromValue !== toValue) {
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      target.setAttribute(key, toValue)
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    }
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  })
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}
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function present (val) {
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  return val != null
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}
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function resolve (source) {
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  return typeof source === 'function' ? source() : source
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}
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