将参数传递给prop函数而不使用箭头函数

Question

I've heard that passing an arrow function as a prop is not ideal because it creates a new function every time which will lead to performance issues. However, I'm not entirely sure how to completely move away from them, as can be seen by the example below:

class Home extends Component {

    onCardPress = (message) =>{
        alert(message)
    }

    render(){
        return(
            <View>
                <Card 
                    onCardPress={this.onCardPress}
                    message="Hello world!"
                />
            </View>
        )
    }
}

class Card extends Component {
    render(){
        const { onCardPress , message } = this.props;
        return(
            <TouchableOpacity
                activeOpacity={0.8}
                onPress={()=>{onCardPress(message)}}
            />
        )
    }
}

I have tried changing onPress in Card to be onPress={onCardPress(message)} , but I know this doesn't work because I am invoking the function rather than passing a function object to the onPress of TouchableOpacity . What is the 'proper' way or best practice to remove the arrow function in TouchableOpacity while still being able to pass the message parameter from the parent component Home ?

Answer 1

If you want to avoid arrow function, you have to use bind() . Arrow functions will automatically bind "this" .

  class Home extends Component {

      constructor(props) {
       super(props);
       this.onCardPress = this.onCardPress.bind(this);
      }

      onCardPress (message) {
        alert(message)
      }

      render(){
        return(
            <View>
                <Card 
                    onCardPress={this.onCardPress}
                    message="Hello world!"
                />
            </View>
        )
      }
  }



class Card extends Component {
    render(){
        const { onCardPress , message } = this.props;
        return(
            <TouchableOpacity
                activeOpacity={0.8}
                onPress={onCardPress(message)}
            />
        )
     }
 }

Answer 2

You could do:

class Card extends Component {
    pressHandler = () => this.props.onCardPress(this.props.message);

    render() {
        return (
            <TouchableOpacity
                activeOpacity={0.8}
                onPress={this.pressHandler.bind(this)}
            />
        );
    } }

Answer 3

As I understand it, the issue lies with calling bind inside of render , or returning the handler from yet another lambda, as this will create a new function each time. The conventional way to get around this problem is to bind your handler functions elsewhere -- like in the constructor. In your case, that could look like this:

constructor(props) {
    ....
    this.onCardPress = this.onCardPress.bind(this);
}

...

<Card 
   onCardPress={this.onCardPress}
   message="Hello world!"
/>

Answer 4

Given you alternative option as arrow function already answered in above post.

class Card extends Component {
   onClick = () => {
      const { onCardPress, message } = this.props;
      onCardPress(message);
    }
    render(){
        const { onCardPress , message } = this.props;
        return(
            <TouchableOpacity
                activeOpacity={0.8}
                onPress={this.onClick}
            />
        )
    }
}

Answer 5

You don't need to pass the message prop because you can access it anywhere in the component. Just supply a function in the onPress prop. And in that function, just access the message prop of the component.

class Home extends Component {
  onCardPress = (message) => {
    alert(message)
  }
  render() {
    return (
      <View>
        <Card
          onCardPress={this.onCardPress}
          message="Hello world!"
        />
      </View>
    )
  }
}

class Card extends Component {
  onClick = () => {
    const { message, onCardPress } = this.props;
    onCardPress(message);
  };
  render() {
    return (
      <TouchableOpacity
        activeOpacity={0.8}
        onPress={this.onClick}
      />
    )
  }
}