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Tim Oltman
7,730 PointsWhen using an arrow function 'this' doesn't work inside the callback. Why?
When I set up the callback function as an arrow function I need to provide an event parameter and use event.target.style.display = 'none'. However, in the solution, they are able to use the 'this' keyword by defining the callback function as an anonymous function with no parameters. I'm just curious why it works this way.
To be specific, the following code results in: Uncaught TypeError: Cannot set property of 'display'.
document.getElementById('begin-game').addEventListener('click', () => {
game.startGame();
this.style.display = 'none';
document.getElementById('play-area').style.opacity = '1';
})
However, only changing the function definition allows the code to work.
document.getElementById('begin-game').addEventListener('click', function() {
game.startGame();
this.style.display = 'none';
document.getElementById('play-area').style.opacity = '1';
})
3 Answers
Rich Donnellan
Treehouse Moderator 27,708 PointsArrow functions don't have their own bindings to this, arguments, super, or new.target keywords. Your second example is exactly what it takes if you do require any of these.
This article might help explain things better: https://www.codementor.io/@dariogarciamoya/understanding-this-in-javascript-with-arrow-functions-gcpjwfyuc
Bobby Verlaan
29,538 PointsPlease mind you can still use an arrow function. Instead of using this, you can use the event object and select the button that was clicked on like this:
const btnStartGame = document.querySelector('button#begin-game');
btnStartGame.addEventListener('click', (e) => {
game.startGame();
e.target.style.display = 'none';
document.getElementById('play-area').style.opacity = '1';
});
Tim Oltman
7,730 PointsThanks for the reply. I thought that an arrow function and an anonymous function were completely equivalent.
Rich Donnellan
Treehouse Moderator 27,708 PointsRich Donnellan
Treehouse Moderator 27,708 PointsQuestion updated with code formatting. Check out the Markdown Cheatsheet below the Add an Answer submission for syntax examples.