异步等待和setTimeout在ReactJS中不起作用

Question

You can see what I've done here .

import "babel-polyfill";
import React from "react";
import ReactDOM from "react-dom";

const asyncFunc = () => {
  return new Promise(resolve => {
    setTimeout(resolve("Gotcha!!!"), 10000);
  });
};

class App extends React.Component {
  state = {
    text: "Fetching..."
  };

  componentDidMount = async () => {
    const text = await asyncFunc();
    this.setState({ text });
  };

  render() {
    return <div className="App">{this.state.text}</div>;
  }
}

The app should show Fetching... first, then shows Gotcha!!! after 10 seconds. But, it's not working. What's my mistake?

Answer 1

The problem is:

setTimeout(resolve("Gotcha!!!"), 10000);

The first argument to setTimeout should be a function . At the moment, you're calling resolve immediately as setTimeout tries to resolve its arguments (synchronously). Instead, pass it a function that then calls resolve :

setTimeout(() => resolve("Gotcha!!!"), 10000);

or

setTimeout(resolve, 10000, "Gotcha!!!");

Answer 2

您需要通过setTimeout一个回调函数，将其更改为此

setTimeout(() => resolve("Gotcha!!!"), 10000);

Answer 3

import "babel-polyfill";
import React from "react";
import ReactDOM from "react-dom";

import "./styles.css";

const asyncFunc = () => {
  return new Promise(resolve => {
    setTimeout(() => resolve("Gotcha!!!"), 10000);
  });
};

class App extends React.Component {
  constructor() {
    super();
    this.state = {
      text: "Fetching..."
    };
  }

  componentDidMount = async () => {
    const newText = await asyncFunc();
    this.setState({ text: newText });
  };

  render() {
    return <div className="App">{this.state.text}</div>;
  }
}

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);