/* @flow */
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import {
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warn,
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remove,
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isObject,
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parsePath,
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_Set as Set,
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handleError,
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noop
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} from '../util/index'
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import { traverse } from './traverse'
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import { queueWatcher } from './scheduler'
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import Dep, { pushTarget, popTarget } from './dep'
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import type { SimpleSet } from '../util/index'
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let uid = 0
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/**
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* A watcher parses an expression, collects dependencies,
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* and fires callback when the expression value changes.
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* This is used for both the $watch() api and directives.
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*/
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export default class Watcher {
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vm: Component;
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expression: string;
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cb: Function;
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id: number;
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deep: boolean;
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user: boolean;
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lazy: boolean;
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sync: boolean;
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dirty: boolean;
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active: boolean;
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deps: Array<Dep>;
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newDeps: Array<Dep>;
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depIds: SimpleSet;
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newDepIds: SimpleSet;
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before: ?Function;
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getter: Function;
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value: any;
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constructor (
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vm: Component,
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expOrFn: string | Function,
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cb: Function,
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options?: ?Object,
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isRenderWatcher?: boolean
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) {
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this.vm = vm
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if (isRenderWatcher) {
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vm._watcher = this
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}
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vm._watchers.push(this)
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// options
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if (options) {
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this.deep = !!options.deep
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this.user = !!options.user
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this.lazy = !!options.lazy
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this.sync = !!options.sync
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this.before = options.before
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} else {
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this.deep = this.user = this.lazy = this.sync = false
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}
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this.cb = cb
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this.id = ++uid // uid for batching
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this.active = true
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this.dirty = this.lazy // for lazy watchers
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this.deps = []
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this.newDeps = []
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this.depIds = new Set()
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this.newDepIds = new Set()
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this.expression = process.env.NODE_ENV !== 'production'
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? expOrFn.toString()
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: ''
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// parse expression for getter
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if (typeof expOrFn === 'function') {
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this.getter = expOrFn
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} else {
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this.getter = parsePath(expOrFn)
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if (!this.getter) {
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this.getter = noop
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process.env.NODE_ENV !== 'production' && warn(
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`Failed watching path: "${expOrFn}" ` +
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'Watcher only accepts simple dot-delimited paths. ' +
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'For full control, use a function instead.',
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vm
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)
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}
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}
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this.value = this.lazy
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? undefined
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: this.get()
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}
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/**
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* Evaluate the getter, and re-collect dependencies.
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*/
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get () {
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pushTarget(this)
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let value
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const vm = this.vm
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try {
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value = this.getter.call(vm, vm)
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} catch (e) {
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if (this.user) {
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handleError(e, vm, `getter for watcher "${this.expression}"`)
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} else {
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throw e
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}
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} finally {
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// "touch" every property so they are all tracked as
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// dependencies for deep watching
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if (this.deep) {
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traverse(value)
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}
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popTarget()
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this.cleanupDeps()
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}
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return value
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}
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/**
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* Add a dependency to this directive.
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*/
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addDep (dep: Dep) {
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const id = dep.id
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if (!this.newDepIds.has(id)) {
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this.newDepIds.add(id)
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this.newDeps.push(dep)
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if (!this.depIds.has(id)) {
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dep.addSub(this)
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}
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}
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}
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/**
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* Clean up for dependency collection.
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*/
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cleanupDeps () {
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let i = this.deps.length
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while (i--) {
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const dep = this.deps[i]
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if (!this.newDepIds.has(dep.id)) {
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dep.removeSub(this)
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}
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}
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let tmp = this.depIds
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this.depIds = this.newDepIds
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this.newDepIds = tmp
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this.newDepIds.clear()
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tmp = this.deps
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this.deps = this.newDeps
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this.newDeps = tmp
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this.newDeps.length = 0
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}
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/**
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* Subscriber interface.
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* Will be called when a dependency changes.
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*/
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update () {
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/* istanbul ignore else */
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if (this.lazy) {
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this.dirty = true
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} else if (this.sync) {
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this.run()
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} else {
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queueWatcher(this)
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}
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}
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/**
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* Scheduler job interface.
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* Will be called by the scheduler.
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*/
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run () {
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if (this.active) {
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const value = this.get()
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if (
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value !== this.value ||
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// Deep watchers and watchers on Object/Arrays should fire even
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// when the value is the same, because the value may
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// have mutated.
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isObject(value) ||
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this.deep
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) {
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// set new value
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const oldValue = this.value
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this.value = value
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if (this.user) {
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try {
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this.cb.call(this.vm, value, oldValue)
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} catch (e) {
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handleError(e, this.vm, `callback for watcher "${this.expression}"`)
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}
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} else {
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this.cb.call(this.vm, value, oldValue)
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}
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}
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}
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}
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/**
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* Evaluate the value of the watcher.
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* This only gets called for lazy watchers.
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*/
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evaluate () {
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this.value = this.get()
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this.dirty = false
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}
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/**
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* Depend on all deps collected by this watcher.
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*/
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depend () {
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let i = this.deps.length
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while (i--) {
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this.deps[i].depend()
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}
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}
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/**
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* Remove self from all dependencies' subscriber list.
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*/
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teardown () {
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if (this.active) {
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// remove self from vm's watcher list
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// this is a somewhat expensive operation so we skip it
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// if the vm is being destroyed.
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if (!this.vm._isBeingDestroyed) {
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remove(this.vm._watchers, this)
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}
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let i = this.deps.length
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while (i--) {
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this.deps[i].removeSub(this)
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}
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this.active = false
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}
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}
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}
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