Access and update a variable on the Angular scope using "this" within a function

Question

Access and update a variable on the Angular scope using "this" within a function

Looking to update a controller to use the "controller as" syntax has presented some challenges. One issue that arose during the transformation process is the inability to access "scope" variables outside of a function. It seems that, based on my understanding, "this" references the object in which it is used.

this.scopeVariable = undefined;

this.fooFunction = function () {
            resource.get()
                .$promise.then(function (result) {
                this.scopeVariable = result.foo;
            });
        };

When attempting to assign a value to scopeVariable using "this", am I actually trying to access an object from within fooFunction? If so, how can I retrieve an object from outside the function while still inside it?

Your input would be greatly appreciated!

javascript angularjs

Answer 1

Answer №1

The reason for this issue is the dynamic nature of the this keyword, which can change its context in different scopes. For example, in a simple object like:

var example = {
    method: function() {
        console.log(this); // => will display "example"
        setTimeout(function() {
            console.log('some random text');
            console.log(this); // => will show the inner function scope instead of "example"
        }, 200)
    }
} 

example.method(); // to see the results

To avoid encountering such problems, you can assign this to a variable that remains constant throughout nested scopes, like so:

this.scopeVariable = undefined;
var self = this;

this.someFunction = function () {
  resource.fetchData()
  .$promise.then(function (result) {
    // Using self. instead of this. ensures the correct context here
    self.scopeVariable = result.data;
  });
};

Answer 2

The reason for this issue is the dynamic nature of the this keyword, which can change its context in different scopes. For example, in a simple object like:

var example = {
    method: function() {
        console.log(this); // => will display "example"
        setTimeout(function() {
            console.log('some random text');
            console.log(this); // => will show the inner function scope instead of "example"
        }, 200)
    }
} 

example.method(); // to see the results

To avoid encountering such problems, you can assign this to a variable that remains constant throughout nested scopes, like so:

this.scopeVariable = undefined;
var self = this;

this.someFunction = function () {
  resource.fetchData()
  .$promise.then(function (result) {
    // Using self. instead of this. ensures the correct context here
    self.scopeVariable = result.data;
  });
};

Answer 3

Answer №2

Storing the reference to the current scope in a variable named that: var that = this:

var that = this;
this.barMethod = function () {
            api.fetchData()
                .$promise.then(function (response) {
                that.dataVariable = response.bar;
            });
        };

Answer 4

Storing the reference to the current scope in a variable named that: var that = this:

var that = this;
this.barMethod = function () {
            api.fetchData()
                .$promise.then(function (response) {
                that.dataVariable = response.bar;
            });
        };

Access and update a variable on the Angular scope using "this" within a function

Answer №1

Answer №2

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