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Freakin' bind() Function


When i started React Native app development, it started just fine. I love how composition is used rather than inheritance. I prefer the functional component, to me it is more familiar than a Javascript Class. It is just a simple f(x) = y.Then, times come when i have to create a click handler in class

class TestScreen extends React.Component {
  state = { text: 'Yo' }

  printYo() {
    this.setState({ text: 'Yoo!!!!!' })

  render() {
    return (
      <View style={{ flex: 1, alignItems: 'center', justifyContent: 'center' }}>
        <Button onPress={this.printYo} title={this.state.text} />

The screen will show your button and the code will run just fine until you click that button and something like this will show

this.setState is not a function ........ this.setState is undefined

The problem is that for whatever reason (i guess it just how Javascript works) in printYo function, the context has changed or to simply put it the this in printYo is not bound to TestScreen class. This is not React specific issue and has been documented in here

The common solution for this is to bind the function in constructor like this

class Listener {
  constructor() {
    // bind the `extract` function
    this.extract = this.extract.bind(this)

  extract() {
    // calling something with `this`

If you gets annoyed easily with this bind function like me, you should try the experimental property initializer syntax like this

 class Listener {
     extract = () => { // calling something with `this` }

Or just a simple big arrow function

class Listener {
    extract(){ // calling something with `this` }

        new Executor().run(() => this.extract())

The two options is simply better and less frustrating for me. Until next time. Cao ~ 👋