javascript - Why do you have to use keyword "this" instead of class name? - Stack Overflow

this is code from a react.js tutorial and the "this" keyword represents the App class. So my question is why can I not just write the class name instead?

import React, { Component } from 'react';
import './App.css';
import Person from './Person/Person';

class App extends Component {

state = {
 persons: [
  { name: 'Max', age: 28 },
  { name: 'Manu', age: 29 },
  { name: 'Stephanie', age: 26 }
 ]
}

render() {
 return (
  <div className="App">
    <h1>Hi, I'm a React App</h1>
    <p>This is reallyyyyyyyy working!</p>
    <button> switch name</button>
    <Person name={App.state.persons[0].name} age={this.state.persons[0].age} />
    <Person name={this.state.persons[1].name} age={this.state.persons[1].age}>My Hobbies: Racing</Person>
    <Person name={this.state.persons[2].name} age={this.state.persons[2].age} />
  </div>
 );
// return React.createElement('div', {className: 'App'}, 
React.createElement('h1', null, 'Hi, I\'m a React App!!!'));
}
}

export default App;

this is code from a react.js tutorial and the "this" keyword represents the App class. So my question is why can I not just write the class name instead?

import React, { Component } from 'react';
import './App.css';
import Person from './Person/Person';

class App extends Component {

state = {
 persons: [
  { name: 'Max', age: 28 },
  { name: 'Manu', age: 29 },
  { name: 'Stephanie', age: 26 }
 ]
}

render() {
 return (
  <div className="App">
    <h1>Hi, I'm a React App</h1>
    <p>This is reallyyyyyyyy working!</p>
    <button> switch name</button>
    <Person name={App.state.persons[0].name} age={this.state.persons[0].age} />
    <Person name={this.state.persons[1].name} age={this.state.persons[1].age}>My Hobbies: Racing</Person>
    <Person name={this.state.persons[2].name} age={this.state.persons[2].age} />
  </div>
 );
// return React.createElement('div', {className: 'App'}, 
React.createElement('h1', null, 'Hi, I\'m a React App!!!'));
}
}

export default App;

• javascript
• reactjs
• this

Share Improve this question Follow asked May 28, 2018 at 3:00 Ryder ThackerRyder Thacker 1,49233 gold badges1414 silver badges3535 bronze badges 2

• Possible duplicate of How does the "this" keyword work? – ASDFGerte Commented May 28, 2018 at 3:12
• You state "the this" keyword represents the App class". The answer to your question is right there in that misconception. The this keyword does not represent the App class. As clearly explained in tens of thousands of tutorials and blog posts and answers right here on SO, it represents the current instance of the App class. – user9315861 Commented May 28, 2018 at 4:08

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2 Answers 2

Sorted by: Reset to default 9

Because in JavaScript, when you specify a class name (in particular, inside a class), you get a reference to the class, not to the current class instance. The instance properties and methods are not available through its class. Meanwhile this represents the current instance.

class App {
    test() {
        console.log(App); // "class App ..."
        console.log(this); // "[object Object]"
        console.log(App.foo()); // "1"
        console.log(this.foo()); // "2"
        console.log(this.constructor.foo()); // "1"; this.constructor is a reference to the current object class
    }

    static foo() {
        return 1;
    }

    foo() {
        return 2;
    }
}

Because

The this keyword refers to the current instance of the class. It can be used to access members from within constructors, instance methods, and instance accessors.

This rule is followed by any Object Oriented programming language. However, If you force your class to take instance with its name then it has to be static (Not the class itself but properties and methods).

For your purpose we can create App class as module

class App {
  hello() { return 'Hello World'; }
}

export let AppInstance = new App ();

Usage

import { AppInstance } from './App';
AppInstance.hello();