Let's suppose I have the following:
(function() {
let myVar = 300;
window.myFunc = function() {
console.log(myVar);
};
})();
Without changing the above code, can you think of a way to change the myVar variable? I mean from the outside, can you do something like:
window.myFunc.__closure__.myVar = 10;
Is this possible?
No, it is not possible because the scope of the variable is the function's block.
The only way of modifying something inside of the closure is thru properties in the current lexical context (in this case the window object).
(function() {
this.myVar = this.myVar || 300;
window.myFunc = function() {
console.log(myVar);
};
})();
myVar = "Ele";
myFunc();You could define a global function that changes the variable:
(function() {
let myVar = 300;
window.myFunc = function() {
console.log(myVar);
};
window.setMyVar = value => {
myVar = value;
};
})();
myFunc();
setMyVar(10);
myFunc();Or you could return setMyVar:
const setMyVar = (function() {
let myVar = 300;
window.myFunc = function() {
console.log(myVar);
};
return value => {
myVar = value;
};
})();
myFunc();
setMyVar(100);
myFunc();
setMyVar closes over the same variables as myFunc, so can change them. ES modules more or less work the same way.The idea of using a closure is to make variable accessible only to a specific scope. If you then want to change it outside of this scope, why not use a class?
eg.
class myClass {
constructor(var) { this._var = var }
set var(arg) { this._var = arg }
yourFunc() { console.log(this._var) }
}
evil()somewhere where this variable is visible, and you can inject some code.