How to wait for last called async method-CodePudding

I'm implementing a simple search bar that calls an asyncronous method which is populating a display list that is to be displayed as the user types. The issue I'm running into is that every key press triggers another call of the async method, and occasionally the earlier key presses will return after the following key presses, resulting in the display array being populated with results that aren't accounting for later key presses.

For example if a user is typing the word "Dog", the async method "search" will trigger three times, once for "D" once for "Do" and once for "Dog". If the results for "D" return after the results for "Dog" (which is likely, given that there are more results for the shorter search strings), then the final array will be populated with all matches of "D", rather than "Dog".

How can make it so that the final results are always from the last called instance of async search method?

CodePudding user response：

This is a common problem solved by Observables, debounce and the switchMap operator. In Angular it is advised to use Obserables instead of async/await.

obserable.pipe(
  debounceTime(200),
  switchMap(input => {
    // return async http call here
  })
).subscribe(result => {
  // update UI
})

The switchMap guarantees that older events are cancelled when the Observable triggers again. So you will always only see the result of the latest request. The debounceTime will limit the amount of requests to a maximum of 1 request per 200 milliseconds.

CodePudding user response：

Async Await Example click here

Or your input like

<input  placeholder="Search" (keyup.backspace)="onSearchKeyUp($event)" (keyup.enter)="onSearchKeyUp($event)">