call function in ajax success callback - ajax

Question

Is it possible to call a function in success callback of ajax request?
For example I have something like that :
constructor(private http: HttpClient,private serviceComposition: CompositionService) { }
[...]
save() {
var isValid = this.isValidCompo();
if (true) {
var toSend = JSON.stringify(this.setupComposition);
$.ajax({
url: "/api/setup/composition/addSetupComposition",
type: 'POST',
dataType: "json",
data: 'setupComposition=' + toSend,
success:function(response){
//console.log("Success Save Composition");
},
error: function(XMLHttpRequest,textStatus,errorThrown){
console.log("Error Save Compo");
}
}).done(function(data){
this.serviceComposition.changeValue(isValid);
})
}
}
I want to call a function of my service (named : changeValue() ) if my ajax request is a success.
But I have this error message : core.js:12632 ERROR TypeError: Cannot read property 'changeValue' of undefined
Do you know if it's possible to resolve that ?

Answer 1

I am suspecting this binding is going wrong in call backs,
prefer using arrow function because of "this" operator binding.
if (true) {
var toSend = JSON.stringify(this.setupComposition);
$.ajax({
url: "/api/setup/composition/addSetupComposition",
type: 'POST',
dataType: "json",
data: 'setupComposition=' + toSend,
success:function(response){
//console.log("Success Save Composition");
},
error: function(XMLHttpRequest,textStatus,errorThrown){
console.log("Error Save Compo");
}
}).done((data) => {
this.serviceComposition.changeValue(isValid);
})
}
if not u can store this reference in a variable and call it
var self = this;
if (true) {
var toSend = JSON.stringify(this.setupComposition);
$.ajax({
url: "/api/setup/composition/addSetupComposition",
type: 'POST',
dataType: "json",
data: 'setupComposition=' + toSend,
success:function(response){
//console.log("Success Save Composition");
},
error: function(XMLHttpRequest,textStatus,errorThrown){
console.log("Error Save Compo");
}
}).done(function(data){
self.serviceComposition.changeValue(isValid);
})
}

Answer 2

Use an arrow function to access this of your parent scope. In your example, this is referring to your jQuery XHR object.
So:
// [parent scope]
$.ajax({
...
}).done((data) => {
// [child scope]
// `this` now refers to [parent scope], so the following is valid
this.serviceComposition.changeValue(isValid);
});
Another common practice prior to arrow functions (ES6) would've been assigning a const self = this; variable in the [parent scope] area to be accessed in the child method. Either method works the same.
Also check out the MDN docs on this. It's a confusing topic for many.