Make variable visible outside callback function - Ionic2

Question

I'm working with ionic2 and inside ngOnInit method of my controller I have this:

ngOnInit()
{
   let a;
   this.myAsyncMethod(function(b))  // this is a callback of an async method defined somewhere before ngOnInit()
   {
       a = String(b);  
   }
}

I'd like to be able to pass variable a to my template and other methods inside the component file.

So I tried in this way:

export class myComponent {
c:string;

constructor(....){ // some stuff }
... other methods 

ngOnInit()
{
   let a;
   this.myAsyncMethod(function(b))
   {
       a = String(b);
       this.c = a; // here I get this error in red: EXCEPTION: TypeError: Cannot set property 'c' of undefined  
   }
   // if I would put this.c = a here I'll get `c` undefined because I'd be outside the callback function and `a` is not defined yet. 
 }

}

in my template.html I'd like to print c variable doing {{c}}

How can I make c visible in both template.html file and in all other methods I have inside mycomponent.ts?

let self = this; then inside the method self.c = a

taguenizy
– taguenizy

2016-09-15 10:15:35 +00:00
Commented Sep 15, 2016 at 10:15 — taguenizy
– taguenizy, Commented Sep 15, 2016 at 10:15

yurzui · Accepted Answer · 2016-09-15 10:01:49Z

2

Use arrow function like:

this.myAsyncMethod((b) => {
  this.c = String(b);
});

This way this will refer to instance of your component.

See also more details about lexical this here:

https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Functions/Arrow_functions#Lexical_this

answered Sep 15, 2016 at 10:01

yurzui

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