如何在没有此类型的对象的类中调用方法

Question

Hi friends I'm making an app which lists users's emails via Gmail API. For this I have a method which lists threads from user account and then messages in that threads gets fetched. My function is as below:

   public listThreads(opt_params){
    gapi.client.load('gmail', 'v1', function(){

        let request = gapi.client.gmail.users.threads.list({
            'userId': 'me',
            'q': opt_params
        });
        request.execute(function(response) {

            $.each(response.threads,  function() {

               let thread_id = this.id;

               this.getThread(thread_id, this.process_thread);
// error appears on above line. which says "this.getThread is not a function" 
            });
        });
});
    }

Error is "this.getThread is not a function". And that is because "this" now refers to response object and it does not refers to class members anymore. But I need to call getThread function. So I need to know if there is any other way to call class functions without this keyword?

Answer 1

You cannot call a typescript method without using this

Instead you should use fat arrow operators (=>) at three places in your code as opposed to function , to retain the context of this .

1. parameter of gapi.client.load()

     gapi.client.load('gmail', 'v1', () => { ...... }); 

2. parameter of request.execute()

    request.execute((response) => { .... }) 

3. parameter of $.each

    $.each(response.threads, () => { let thread_id = this.id; this.getThread(thread_id, this.process_thread); // this should be accessible here }); 

Answer 2

Because the context, this is lost in the callback. Use arrow functions in typescript to preserve the context!

request.execute().then((response)=> { // here you will have access to 'this' })