Angular: Issue with subscribed variable visibility on screen

I am currently developing user management functionality. When a button is clicked, the goal is to save a new user and display an incoming password stored in the system. Below is a snippet of my code:

onClick() {
/*Code to populate the newUser variable from the form goes here*/
this.store.dispatch(new AddUser(this.newUser)) 
    this.store.select(userFeature.getPassword).subscribe(
      pass => {
      this.temp = pass; //Previously tried using this.password here with no success
    })
    setTimeout(() => {
      this.pause();
    }, 5000);
    //this.password = "Stuff" <-- This works correctly
    this.password = temp //This executes despite the previous wait
}

pause(){
    if(this.temp === null){
        setTimeout(() => {
          this.pause();
        }, 500);
        console.log("Waiting...")
      }
}

Within my HTML, I utilize {{password}} within a simple span element.

EDIT: Issue resolved! The solution involved using ChangeDetectorRef.

this.store.dispatch(new AddUser(this.newUser))
    this.store.select(userFeature.getPassword).subscribe(
      pass => {
      this.password = pass;
      this.cd.detectChanges();
      });

Answer №1

There are several issues present in the provided code snippet, with a primary focus on understanding synchronous and asynchronous execution.

Synchronous execution refers to code being executed line by line from top to bottom within a block. For example:

// Start of block 

let variable = 1; // The variable will have a value of 1 here
variable = variable + 1; // The variable will now hold a value of 2

// End of block

Contrastingly, asynchronous execution involves actions not necessarily occurring sequentially. An illustrative example using setTimeout showcases this concept, where multiple asynchronous operations can be performed independently:

// Start of block 1

let variable = 1; // The variable is set to 1 here

setTimeout(() => {
   // Start of block 2

   variable = variable + 1; // Variable becomes 3 here
   variable = variable + 1; // Variable further increases to 4 here

   // End of block 2
}, 1000);

variable = variable + 1; // This results in the variable being 2

// End of block 1

In such scenarios, each block executes autonomously without waiting for others to complete, thus termed non-blocking. NgRx implement these concepts, where functions like dispatch and select run asynchronously triggering subsequent actions. It's crucial to acknowledge that their order of execution may vary resulting in undefined variables if accessed prematurely.

To prevent such occurrences, wrapping logic around checks ensures values are properly initialized before use:

this.store.select(userFeature.getPassword).subscribe(
  pass => {
   if(pass) {
     this.temp = pass;
     /* Utilize the password value */
   }
  }
)

// OR 

this.store.select(userFeature.getPassword).pipe(
  filter((pass) => !!pass),
  tap((pass) => {
    this.temp = pass;
     /* Utilize the password value */
  }),
).subscribe()

In complex scenarios, synchronization tokens may be required in Actions and State management to ensure correct data linkage for specific actions and side effects.

Avoid employing this.cd.detectChanges(); for this purpose

NOTE

The address made concerns the snippet specifically. Consider revisiting the functional requirement underlying your approach and remember to unsubscribe from selections to prevent memory leaks.

Answer №2

After incorporating a ChangeDetectorRef, I made sure to invoke it following the assignment of 'pass'.

    this.store.select(userFeature.getPassword).subscribe(
      pass => {
      this.password = pass;
      this.cd.detectChanges();
      });

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