watcher.js

var _ = require('./util')
var config = require('./config')
var Observer = require('./observer')
var expParser = require('./parse/expression')
var Batcher = require('./batcher')

var batcher = new Batcher()
var uid = 0

/**
 * A watcher parses an expression, collects dependencies,
 * and fires callback when the expression value changes.
 * This is used for both the $watch() api and directives.
 *
 * @param {Vue} vm
 * @param {String} expression
 * @param {Function} cb
 * @param {Array} [filters]
 * @param {Boolean} [needSet]
 * @param {Boolean} [deep]
 * @constructor
 */

function Watcher (vm, expression, cb, filters, needSet, deep) {
  this.vm = vm
  vm._watcherList.push(this)
  this.expression = expression
  this.cbs = [cb]
  this.id = ++uid // uid for batching
  this.active = true
  this.deep = deep
  this.deps = Object.create(null)
  // setup filters if any.
  // We delegate directive filters here to the watcher
  // because they need to be included in the dependency
  // collection process.
  this.readFilters = filters && filters.read
  this.writeFilters = filters && filters.write
  // parse expression for getter/setter
  var res = expParser.parse(expression, needSet)
  this.getter = res.get
  this.setter = res.set
  this.value = this.get()
}

var p = Watcher.prototype

/**
 * Add a binding dependency to this directive.
 *
 * @param {Binding} binding
 */

p.addDep = function (binding) {
  var id = binding.id
  if (!this.newDeps[id]) {
    this.newDeps[id] = binding
    if (!this.deps[id]) {
      this.deps[id] = binding
      binding.addSub(this)
    }
  }
}

/**
 * Evaluate the getter, and re-collect dependencies.
 */

p.get = function () {
  this.beforeGet()
  var vm = this.vm
  var value
  try {
    value = this.getter.call(vm, vm)
  } catch (e) {}
  // use JSON.stringify to "touch" every property
  // so they are all tracked as dependencies for
  // deep watching
  if (this.deep) JSON.stringify(value)
  value = _.applyFilters(value, this.readFilters, vm)
  this.afterGet()
  return value
}

/**
 * Set the corresponding value with the setter.
 *
 * @param {*} value
 */

p.set = function (value) {
  var vm = this.vm
  value = _.applyFilters(
    value, this.writeFilters, vm, this.value
  )
  try {
    this.setter.call(vm, vm, value)
  } catch (e) {}
}

/**
 * Prepare for dependency collection.
 */

p.beforeGet = function () {
  Observer.target = this
  this.newDeps = {}
}

/**
 * Clean up for dependency collection.
 */

p.afterGet = function () {
  Observer.target = null
  for (var id in this.deps) {
    if (!this.newDeps[id]) {
      this.deps[id].removeSub(this)
    }
  }
  this.deps = this.newDeps
}

/**
 * Subscriber interface.
 * Will be called when a dependency changes.
 */

p.update = function () {
  if (config.async) {
    batcher.push(this)
  } else {
    this.run()
  }
}

/**
 * Batcher job interface.
 * Will be called by the batcher.
 */

p.run = function () {
  if (this.active) {
    var value = this.get()
    if (
      (typeof value === 'object' && value !== null) ||
      value !== this.value
    ) {
      var oldValue = this.value
      this.value = value
      var cbs = this.cbs
      for (var i = 0, l = cbs.length; i < l; i++) {
        cbs[i](value, oldValue)
        // if a callback also removed other callbacks,
        // we need to adjust the loop accordingly.
        var removed = l - cbs.length
        if (removed) {
          i -= removed
          l -= removed
        }
      }
    }
  }
}

/**
 * Add a callback.
 *
 * @param {Function} cb
 */

p.addCb = function (cb) {
  this.cbs.push(cb)
}

/**
 * Remove a callback.
 *
 * @param {Function} cb
 */

p.removeCb = function (cb) {
  var cbs = this.cbs
  if (cbs.length > 1) {
    var i = cbs.indexOf(cb)
    if (i > -1) {
      cbs.splice(i, 1)
    }
  } else if (cb === cbs[0]) {
    this.teardown()
  }
}

/**
 * Remove self from all dependencies' subcriber list.
 */

p.teardown = function () {
  if (this.active) {
    // remove self from vm's watcher list
    // we can skip this if the vm if being destroyed
    // which can improve teardown performance.
    if (!this.vm._isBeingDestroyed) {
      var list = this.vm._watcherList
      list.splice(list.indexOf(this))
    }
    for (var id in this.deps) {
      this.deps[id].removeSub(this)
    }
    this.active = false
    this.vm = this.cbs = this.value = null
  }
}

module.exports = Watcher