在TypeScript中，如何在本地更改全局变量的值？

Question

public login(username: string, password: string): string {

const options = {}; 
let flag = 1;  
this.auth0.client.login({realm: 'Username-Password-Authentication', username, password}, (err,authResult) => {
  if(err) {
    flag = 1;
    console.log(err);   
    return;
  }
  else if (authResult && authResult.accessToken && authResult.idToken) {
    let flag = 0;
    this.setSession(authResult);
    alert("Flag: " + flag);
  }
  else {  
    console.log(err); 
    return;
    //alert('Error: ${err.error_description}. Check the console for further details.'); console.log(username,password)
}
});
if(flag == 0) {
  alert(flag);
  return "Invalid credentials";
}
}

In this code block the "if(flag == 0)" statement is never executed, since the global value is 1. How do I change the global value of flag?

Answer 1

Your main problem is that:

this.auth0.client.login()

is asynchronous. That's why you are passing it a callback function.

What this means is that the order of operations is:

1. let flag = 1 ;
2. start the async operation with this.auth0.client.login()
3. test if (flag == 0) // which of course doesn't fire because flag still equals 1
4. async callbacks fire and you try to set flag, but it's too late.

You need to somehow move the logic into the async side of things. This might require that your main login() accepts a callback that you can fire when is.auth0.client.login() is done or use a promise.

One way or another your if(flag == 0) {} test needs to be inside the callback. And you probably don't want to create a new local variable inside the else if -- I think you want flag = 0; not let flag = 0;