调用登录功能只需按“ enter”键一次

Question

I'm working on a login function right now. I put my enterKey function in the input, and my aim is to call the login function when the user press the enter key. It works fine if there's nothing in the input area, however, I find that if I have some characters in the input text area, the function will be called multiple times and give multiple error messages. For example, if I have N characters in the input, I will receive (N+1) error messages after press the enter key. Here is my code:

 enterKeyPress() {
    window.addEventListener("keypress", e => {
      if (e.keyCode === 13) {
        console.log('enter key pressed!'); // I will receive this msg (N+1) times when there're N characters in the input text area 
        e.preventDefault();
        this.loginUser(); // this is the login function I want to call after press enter key, but just once per press
      }
    });
  }
 render() {
    return(
      <Input
         type="password"
         placeholder="Password"
         onChange={e =>
            this.setState({ password: e.target.value })
         }
         onKeyPress={this.enterKeyPress()}
      />
    );
}

Can anyone help me with this?

Answer 1

From some quick Googling, I think this might do what you need:

enterKeyPress(e) {
    if (e.keyCode === 13) {
      console.log('enter key pressed!'); // I will receive this msg (N+1) times when there're N characters in the input text area 
      e.preventDefault();
      this.loginUser(); // this is the login function I want to call after press enter key, but just once per press
    });
}
render() {
    return(
      <Input
         type="password"
         placeholder="Password"
         onChange={e =>
            this.setState({ password: e.target.value })
         }
         onKeyPress={this.enterKeyPress}
      />
    );
}

onKeyPress already does what the event listener you're trying to add does, so just pass it the keypress event directly instead.

Answer 2

Like @Ronnie has pointed out in the comments, you are adding a new event listener every time the onKeyPress function is triggered on the component, which causes the problems. Since onKeyPress event already passes the event as an argument (similar to onClick event), you can access the keyCode from there.

You can change your enterKeyPress function to the following:

enterKeyPress(e) {
    if (e.keyCode === 13) {
      console.log('enter key pressed!'); 
      e.preventDefault();
      this.loginUser();
    }
  }

Answer 3

Event listeners aren't necessary in this case.

First thing, adjust enterKeyPress to not create an event listener. If you haven't bound the function in your constructor, then you can convert enterKeyPress to an arrow function:

enterKeyPress = (e) => {
    if (e.keyCode === 13) {
        console.log('enter key pressed!');
        e.preventDefault();
        this.loginUser();
    });
}

Converting enterKeyPress to an arrow function is one way to scope the function to the component. Another option is binding the function in your constructor or in your render function, which is well documented elsewhere. If you've already bound the function in your constructor (you haven't included it here), then you can ignore that part.

Second, adjust your onKeyPress prop to pass the function rather than calling it:

<Input
    type="password"
    placeholder="Password"
    onChange={e =>
        this.setState({ password: e.target.value })
    }
    onKeyPress={this.enterKeyPress}
/>

It's also worth noting that there's another general JavaScript mistake here: using an anonymous callback function in your event listener. By using an anonymous function, you're enabling the same function to be added multiple times, since a different function reference is generated each time. This also means that you won't be able to remove it later, since you'll require the function reference to do so.

Again, you don't need an event listener here, but if you did , you should probably define the callback in the component scope, so that you can remove it at some later point. A common pattern for using event listeners is as follows:

handleKeyPress = (e) => {
    if (e.keyCode === 13) {
      console.log('enter key pressed!'); 
      e.preventDefault();
      this.loginUser();
    });
} 

componentDidMount() {
    window.addEventListener("keypress", this.handleKeyPress);
}

componentWillUnmount() {
    window.removeEventListener("keypress", this.handleKeyPress);
}