How can parameters be accessed outside the $timeout callback in Angular?

Question

How can parameters be accessed outside the $timeout callback in Angular?

My code includes a timeout loop structured like this:

var somedata = {
        autoRefreshInterval: 300,
        autoRefreshInSec: 300,
        myTimeout: null,
        doRefresh: _doRefresh,
        onTimeout: function () {
            this.autoRefreshInSec--;
            if (this.autoRefreshInSec <= 0) {
                this.autoRefreshInSec = this.autoRefreshInterval; 
                this.doRefresh();
            }
            this.myTimeout = $timeout(this.onTimeout, 1000);
        },
        startTimer: function () {
            this.autoRefreshInSec = this.autoRefreshInterval;
            this.myTimeout = $timeout(this.onTimeout, 1000);
        },
        stopTimer: function () {
            $timeout.cancel(this.myTimeout);
        },
    }

It seems that the use of "this" within the onTimeout callback function is causing issues, whereas it functions correctly in startTimer and stopTimer. How can I resolve this?

UPDATE:

Because the context of "this" is lost inside onTimeout as explained in one of the answers below, I attempted to pass it in like this:

onTimeout: function (self) {
    self.autoRefreshInSec--;
    if (self.autoRefreshInSec <= 0) {
        self.autoRefreshInSec = self.autoRefreshInterval;  
        self.doRefresh();
    }
    self.myTimeout = $timeout(self.onTimeout(self), 1000);
},
startTimer: function () {
    this.autoRefreshInSec = this.autoRefreshInterval;
    this.myTimeout = $timeout(this.onTimeout(this), 1000);
},

Interestingly, while debugging the code appeared to work. However, upon removing breakpoints, self.doRefresh() starts executing continuously. Why is this happening?

UPDATE 2:

To demonstrate the issue, I have created a JSFiddle at http://jsfiddle.net/qY86q/1.

javascript angularjs timeout

Answer 1

Answer №1

Function.prototype.bind()

The bind() function is used to create a new function where the value of 'this' keyword is set to a specified value, along with any additional arguments that are passed when the new function is called.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind

Solution tailored for your scenario

angular.module('myApp', [])
  .service('timerService', function($timeout) {
    var _timer = {
      autoRefreshInterval: 300,
      autoRefreshInSec: 300,
      myTimeout: null,
      onTimeout: function() {
        this.autoRefreshInSec -= 1;
        if (this.autoRefreshInSec <= 0) {
          this.autoRefreshInSec = this.autoRefreshInterval;
          console.log('refreshing');
        }
        console.log('time: ', this.autoRefreshInSec);
        this.myTimeout = $timeout(this.onTimeout.bind(this), 1000);
      },
      startTimer: function() {
        if (this.myTimeout) {
          this.stopTimer(this.myTimeout)
        }
        this.autoRefreshInSec = this.autoRefreshInterval;
        this.myTimeout = $timeout(this.onTimeout.bind(this), 1000);
      },
      stopTimer: $timeout.cancel // see note(1)
    };
    var context = {
      timer: _timer
    };
    return context;
  }).controller('PrefsCtrl', function PrefsCtrl($scope, timerService) {
    $scope.timer = timerService.timer;
  })

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>

<div ng-app="myApp">
  <div ng-controller="PrefsCtrl">
    <button ng-click="timer.startTimer()">Click to Start or Reset Timer</button>
    <div>{{timer.autoRefreshInSec}}</div>
  </div>
</div>

note(1), this is shorcut for

stopTimer: function(timer) {
   $timeout.cancel(timer)
}

Answer 2

Function.prototype.bind()

The bind() function is used to create a new function where the value of 'this' keyword is set to a specified value, along with any additional arguments that are passed when the new function is called.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind

Solution tailored for your scenario

angular.module('myApp', [])
  .service('timerService', function($timeout) {
    var _timer = {
      autoRefreshInterval: 300,
      autoRefreshInSec: 300,
      myTimeout: null,
      onTimeout: function() {
        this.autoRefreshInSec -= 1;
        if (this.autoRefreshInSec <= 0) {
          this.autoRefreshInSec = this.autoRefreshInterval;
          console.log('refreshing');
        }
        console.log('time: ', this.autoRefreshInSec);
        this.myTimeout = $timeout(this.onTimeout.bind(this), 1000);
      },
      startTimer: function() {
        if (this.myTimeout) {
          this.stopTimer(this.myTimeout)
        }
        this.autoRefreshInSec = this.autoRefreshInterval;
        this.myTimeout = $timeout(this.onTimeout.bind(this), 1000);
      },
      stopTimer: $timeout.cancel // see note(1)
    };
    var context = {
      timer: _timer
    };
    return context;
  }).controller('PrefsCtrl', function PrefsCtrl($scope, timerService) {
    $scope.timer = timerService.timer;
  })

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>

<div ng-app="myApp">
  <div ng-controller="PrefsCtrl">
    <button ng-click="timer.startTimer()">Click to Start or Reset Timer</button>
    <div>{{timer.autoRefreshInSec}}</div>
  </div>
</div>

note(1), this is shorcut for

stopTimer: function(timer) {
   $timeout.cancel(timer)
}

Answer 3

Answer №2

There seems to be a slight complication with the javascript binding in this case.

Here is a possible solution:

var customData;  // now we can reference this in the angular.bind function
customData = {
    onEvent: angular.bind(customData, function () {
        this.count--;
        if (this.count <= 0) {
            this.count = this.interval;
            this.handleEvent();
        }
        this.timer = $timeout(this.onEvent, 1000);
    })
}

This method will ensure that the context of this inside the callback function is specifically tied to customData.

Answer 4

There seems to be a slight complication with the javascript binding in this case.

Here is a possible solution:

var customData;  // now we can reference this in the angular.bind function
customData = {
    onEvent: angular.bind(customData, function () {
        this.count--;
        if (this.count <= 0) {
            this.count = this.interval;
            this.handleEvent();
        }
        this.timer = $timeout(this.onEvent, 1000);
    })
}

This method will ensure that the context of this inside the callback function is specifically tied to customData.

How can parameters be accessed outside the $timeout callback in Angular?

Answer №1

Function.prototype.bind()

Solution tailored for your scenario

Answer №2

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