TypeError: Cannot set property 'ar' of undefined

Question

i set variable ar at the first. like

export class HomePage {
ar:any;
 ... 
 ...
constructor( ...){
 ar=new Array();
...
this.loadEvent();
}

and then, on triggered function of constructor,

I tweaked above function to below

Why can't I put values from firebase to variable ar?

Hey it's generally a better idea to post your actual code rather than screenshots of it. It makes it easier for people to answer your question. — m0meni, Sep 17 '18 at 23:23
Also since it looks like you're using VSCode, you might want to install this: https://marketplace.visualstudio.com/items?itemName=esbenp.prettier-vscode extension that'll format your code for you. Right now it's a little hard to read — m0meni, Sep 17 '18 at 23:25

score 2 · Accepted Answer · answered Sep 17 '18 at 23:22

That's happening because this inside your function passed to .then is different from this outside your function. Read https://yehudakatz.com/2011/08/11/understanding-javascript-function-invocation-and-this/ for a good explanation on why.

To fix this instead of

function (snapshot) {}

you need to do

(snapshot) => {}

which maintains the value of this from the outer scope.

1 Answers1