Rxjs 使用主题在反应文本输入组件上去抖动不会在无状态/功能组件上批量输入文本

Question

I'm trying to dive deeper into rxjs and found an issue where the input field I'm trying to debounce dispatches an event on every keypress, the debounce only holds the output but results in a tree like:

a
as(delay - waits 200ms, then fires the rest synchronously)
asd
asdf
asdfg 
....

The same code works as expected in a class component( https://stackoverflow.com/a/44300853/1356046 ) but cannot understand why it doesn't work with stateless components. Here's an example: https://stackblitz.com/edit/react-hzhrmf - you can see the useState update fires for every keystroke.

Thanks a lot.

Answer 1

React continuously calls your function to render the component. Therefore the Subject is continuously recreated.

Using a factory with useState to keep the subject and working with useEffect to make sure the subscription is only made once should fix your issue.

Something like this:

import React, { Component, useState, useEffect, useRef } from 'react';
import { render } from 'react-dom';
import { debounceTime, map, tap, distinctUntilChanged } from 'rxjs/operators';
import { fromEvent, Subject } from 'rxjs';

import './style.css';
const App = props => {
  const [queryName, setQueryName] = useState("");
  const [debouncedName, setDebouncedName] = useState("");
  const [onSearch$] = useState(()=>new Subject());
  useEffect(() => {
    const subscription = onSearch$.pipe(
      debounceTime(400),
      distinctUntilChanged(),
      tap(a => console.log(a))
    ).subscribe(setDebouncedName);
  }, [])
  const handleSearch = e => {
    setQueryName(e.target.value);
    onSearch$.next(e.target.value);
  };

  return (
    <div>
      <input
        placeholder="Search Tags"
        value={queryName}
        onChange={handleSearch}
      />
      <p>Debounced: {debouncedName}</p>
    </div>
  );
}

render(<App />, document.getElementById('root'));

Answer 2

Here is a version as custom Hook as this might be used multiple times in a form and can otherwise clutter your code.

function useDebounce<T = any>(time: number, defaultValue: T): [T, (v: T) => void] {
  let [value, setValue] = React.useState<T>(defaultValue);
  let [value$] = React.useState(() => new Subject<T>());
  React.useEffect(() => {
    let sub = value$.pipe(debounceTime(time)).subscribe(setValue);
    return () => sub.unsubscribe();
  }, [time, value$]);
 return [value, (v) => value$.next(v)];
}

//useage: 
let [value,setValue] = useDebounce(200,"");