I have a module pattern with a variable setting the currentPlayer to 1. I use a function expression to toggle that variable
const game = (() => {
let currentPlayer = 1;
const toggleCurrentPlayer = () => {
if (currentPlayer == 1){
currentPlayer = 2 ;
}
else {
currentPlayer = 1;
}
};
return {currentPlayer, toggleCurrentPlayer};
})();
If I run game.currentPlayer
it logs 1, I then run game.toggleCurrentPlayer()
, and it doesn't change currentPlayer
as intended, it still returns 1.
However, changing the toggleCurrentPlayer()
function using this
, seems to be able to change the variable successfully
function toggleCurrentPlayer(){
if (this.currentPlayer == 1){
this.currentPlayer=2;
}
else if (this.currentPlayer == 2){
this.currentPlayer=1;
}
};
I know function declarations and function expressions have different meanings for the keyword this
, but why would the toggleCurrentPlayer()
only work properly with the this
keyword and not be able to set the variable on its own?
When the function does
return {currentPlayer, toggeleCurrentPlayer};
It copies the initial value of the currentPlayer
variable into the object.
The returned object contains the value of the variable, not a reference to the variable itself. Reassigning the variable has no effect on the object.
What you can do instead is create an object inside the function, and modify that.
const game = (() => {
let obj = {
currentPlayer: 1,
toggleCurrentPlayer: () => {
if (obj.currentPlayer == 1) {
obj.currentPlayer = 2;
} else {
obj.currentPlayer = 1;
}
}
};
return obj;
})();
console.log(game.currentPlayer);
game.toggleCurrentPlayer();
console.log(game.currentPlayer);
Another way to do it is with a getter function that retrieves the variable.
const game = (() => {
let currentPlayer = 1;
const toggleCurrentPlayer = () => {
if (currentPlayer == 1){
currentPlayer = 2 ;
}
else {
currentPlayer = 1;
}
};
const getCurrentPlayer = () => currentPlayer
return {getCurrentPlayer, toggleCurrentPlayer};
})();
console.log(game.getCurrentPlayer());
game.toggleCurrentPlayer();
console.log(game.getCurrentPlayer());