What could cause the variable "this" in a function within an AngularJS service to be undefined?

Question

What could cause the variable "this" in a function within an AngularJS service to be undefined?

Why is the inside function undefined in the AngularJS service?

.service('SliceService', function () {
    var self = this;

    var Slice = function(intervals, intervalSpan) {
        self.activeSlice = [];
        self.hasNext = true;
        self.hasPrevious = false;
        self.intervals = intervals;
        self.intervalSpan = intervalSpan;
    }

    Slice.prototype.findIntervalIndex = function (time, slice) {
        slice = slice || self.intervals;
        return _.findIndex(slice, function (o) {
            return o.time === time;
        });
    };

    return Slice;

})

.controller('myController', ['SliceService', function(SliceService) {
    SliceService([arr], 12);
    SliceService.findINtervalIndex(time);
}])

When using it in a controller, the error

TypeError: Cannot set property 'activeSlice' of undefined

occurs.

-

Update

Thank you, everyone! I have made changes to my example to better explain what I am trying to achieve. However, I am now encountering a

TypeError: SliceService.findIntervalIndex is not a function

. Maybe a service is not the best approach for my task?

javascript angularjs prototype this

Answer 1

Answer №1

To ensure the value of "this" is preserved within the anonymous scope, consider saving it in a variable before accessing it:

(function(){
    'use strict';

    angular.module('myServices').service('SliceService', function () {
        var context = this;

        var Slice = function(intervals, intervalSpan) {
            context.activeSlice = [];
            context.hasNext = true;
            context.hasPrevious = false;
            context.intervals = intervals;
            context.intervalSpan = intervalSpan;
        }

        return Slice;
    });
}());

Using Bind:

    angular.module('myServices').service('SliceService', function () {
        var Slice = function(intervals, intervalSpan) {
            this.activeSlice = [];
            this.hasNext = true;
            this.hasPrevious = false;
            this.intervals = intervals;
            this.intervalSpan = intervalSpan;
        }.bind(this);

        return Slice;
    });

Note: using arrow function of javascript ES6 makes sure that this always points to the same context. so you could replace regular function with arrow function. This is however not universally supported without transpiling.

service('SliceService', ()=>{ 
 // operations
}

Answer 2

To ensure the value of "this" is preserved within the anonymous scope, consider saving it in a variable before accessing it:

(function(){
    'use strict';

    angular.module('myServices').service('SliceService', function () {
        var context = this;

        var Slice = function(intervals, intervalSpan) {
            context.activeSlice = [];
            context.hasNext = true;
            context.hasPrevious = false;
            context.intervals = intervals;
            context.intervalSpan = intervalSpan;
        }

        return Slice;
    });
}());

Using Bind:

    angular.module('myServices').service('SliceService', function () {
        var Slice = function(intervals, intervalSpan) {
            this.activeSlice = [];
            this.hasNext = true;
            this.hasPrevious = false;
            this.intervals = intervals;
            this.intervalSpan = intervalSpan;
        }.bind(this);

        return Slice;
    });

Note: using arrow function of javascript ES6 makes sure that this always points to the same context. so you could replace regular function with arrow function. This is however not universally supported without transpiling.

service('SliceService', ()=>{ 
 // operations
}

Answer 3

Answer №2

Big shoutout to @SeedyROM and some helpful Google searches on angular services. With their assistance, I was able to resolve all the issues I was facing...

angular.module('vpower.services').service('SliceService', function () {
    this.activeSlice = [];
    this.hasNext = true;
    this.hasPrevious = false;
    this.intervals = [];
    this.intervalSpan = 12;

    this.findIntervalIndex = function (time, slice) {
        var curTime;
        slice = slice || this.intervals;
        return _.findIndex(slice, function (o) {
                curTime = o.time._i || o.time;
            return curTime === time;
        });
    };

It became clear to me that I had some misconceptions about how services operate.

Answer 4

Big shoutout to @SeedyROM and some helpful Google searches on angular services. With their assistance, I was able to resolve all the issues I was facing...

angular.module('vpower.services').service('SliceService', function () {
    this.activeSlice = [];
    this.hasNext = true;
    this.hasPrevious = false;
    this.intervals = [];
    this.intervalSpan = 12;

    this.findIntervalIndex = function (time, slice) {
        var curTime;
        slice = slice || this.intervals;
        return _.findIndex(slice, function (o) {
                curTime = o.time._i || o.time;
            return curTime === time;
        });
    };

It became clear to me that I had some misconceptions about how services operate.

What could cause the variable "this" in a function within an AngularJS service to be undefined?

Update

Answer №1

Answer №2

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