directive.js

var _ = require('./util')
var Watcher = require('./watcher')
var expParser = require('./parsers/expression')
function noop () {}

/**
 * A directive links a DOM element with a piece of data,
 * which is the result of evaluating an expression.
 * It registers a watcher with the expression and calls
 * the DOM update function when a change is triggered.
 *
 * @param {String} name
 * @param {Node} el
 * @param {Vue} vm
 * @param {Object} descriptor
 *                 - {String} name
 *                 - {Object} def
 *                 - {String} expression
 *                 - {Array<Object>} [filters]
 *                 - {Boolean} literal
 *                 - {String} attr
 *                 - {String} raw
 * @param {Object} def - directive definition object
 * @param {Vue} [host] - transclusion host component
 * @param {Object} [scope] - v-for scope
 * @param {Fragment} [frag] - owner fragment
 * @constructor
 */

function Directive (descriptor, vm, el, host, scope, frag) {
  this.vm = vm
  this.el = el
  // copy descriptor properties
  this.descriptor = descriptor
  this.name = descriptor.name
  this.expression = descriptor.expression
  this.arg = descriptor.arg
  this.modifiers = descriptor.modifiers
  this.filters = descriptor.filters
  this.literal = this.modifiers && this.modifiers.literal
  // private
  this._locked = false
  this._bound = false
  this._listeners = null
  // link context
  this._host = host
  this._scope = scope
  this._frag = frag
}

/**
 * Initialize the directive, mixin definition properties,
 * setup the watcher, call definition bind() and update()
 * if present.
 *
 * @param {Object} def
 */

Directive.prototype._bind = function () {
  var name = this.name
  var descriptor = this.descriptor

  // remove attribute
  if (
    (name !== 'cloak' || this.vm._isCompiled) &&
    this.el && this.el.removeAttribute
  ) {
    var attr = descriptor.attr || ('v-' + name)
    this.el.removeAttribute(attr)
  }

  // copy def properties
  var def = descriptor.def
  if (typeof def === 'function') {
    this.update = def
  } else {
    _.extend(this, def)
  }

  // initial bind
  if (this.bind) {
    this.bind()
  }

  if (this.literal) {
    this.update && this.update(descriptor.raw)
  } else if (
    this.expression &&
    (this.update || this.twoWay) &&
    !this._checkStatement()
  ) {
    // wrapped updater for context
    var dir = this
    if (this.update) {
      this._update = function (val, oldVal) {
        if (!dir._locked) {
          dir.update(val, oldVal)
        }
      }
    } else {
      this._update = noop
    }
    var preProcess = this._preProcess
      ? _.bind(this._preProcess, this)
      : null
    var postProcess = this._postProcess
      ? _.bind(this._postProcess, this)
      : null
    var watcher = this._watcher = new Watcher(
      this.vm,
      this.expression,
      this._update, // callback
      {
        filters: this.filters,
        twoWay: this.twoWay,
        deep: this.deep,
        preProcess: preProcess,
        postProcess: postProcess,
        scope: this._scope
      }
    )
    // v-model with inital inline value need to sync back to
    // model instead of update to DOM on init. They would
    // set the afterBind hook to indicate that.
    if (this.afterBind) {
      this.afterBind()
    } else if (this.update) {
      this.update(watcher.value)
    }
  }
  this._bound = true
}

/**
 * Check if the directive is a function caller
 * and if the expression is a callable one. If both true,
 * we wrap up the expression and use it as the event
 * handler.
 *
 * e.g. on-click="a++"
 *
 * @return {Boolean}
 */

Directive.prototype._checkStatement = function () {
  var expression = this.expression
  if (
    expression && this.acceptStatement &&
    !expParser.isSimplePath(expression)
  ) {
    var fn = expParser.parse(expression).get
    var scope = this._scope || this.vm
    var handler = function () {
      fn.call(scope, scope)
    }
    if (this.filters) {
      handler = this.vm._applyFilters(handler, null, this.filters)
    }
    this.update(handler)
    return true
  }
}

/**
 * Check for an attribute directive param, e.g. lazy
 *
 * @param {String} name
 * @return {String}
 */

Directive.prototype.param = function (name) {
  var param = _.attr(this.el, name)
  if (param != null) {
    param = (this._scope || this.vm).$interpolate(param)
  } else {
    param = _.getBindAttr(this.el, name)
    if (param != null) {
      param = (this._scope || this.vm).$eval(param)
      process.env.NODE_ENV !== 'production' && _.log(
        'You are using bind- syntax on "' + name + '", which ' +
        'is a directive param. It will be evaluated only once.'
      )
    }
  }
  return param
}

/**
 * Set the corresponding value with the setter.
 * This should only be used in two-way directives
 * e.g. v-model.
 *
 * @param {*} value
 * @public
 */

Directive.prototype.set = function (value) {
  /* istanbul ignore else */
  if (this.twoWay) {
    this._withLock(function () {
      this._watcher.set(value)
    })
  } else if (process.env.NODE_ENV !== 'production') {
    _.warn(
      'Directive.set() can only be used inside twoWay' +
      'directives.'
    )
  }
}

/**
 * Execute a function while preventing that function from
 * triggering updates on this directive instance.
 *
 * @param {Function} fn
 */

Directive.prototype._withLock = function (fn) {
  var self = this
  self._locked = true
  fn.call(self)
  _.nextTick(function () {
    self._locked = false
  })
}

/**
 * Convenience method that attaches a DOM event listener
 * to the directive element and autometically tears it down
 * during unbind.
 *
 * @param {String} event
 * @param {Function} handler
 */

Directive.prototype.on = function (event, handler) {
  _.on(this.el, event, handler)
  ;(this._listeners || (this._listeners = []))
    .push([event, handler])
}

/**
 * Teardown the watcher and call unbind.
 */

Directive.prototype._teardown = function () {
  if (this._bound) {
    this._bound = false
    if (this.unbind) {
      this.unbind()
    }
    if (this._watcher) {
      this._watcher.teardown()
    }
    var listeners = this._listeners
    if (listeners) {
      for (var i = 0; i < listeners.length; i++) {
        _.off(this.el, listeners[i][0], listeners[i][1])
      }
    }
    this.vm = this.el =
    this._watcher = this._listeners = null
  }
}

module.exports = Directive