How to write code to check if the value of a variable has changed in real time (JavaScript)

Question

I would like to know how to write a script that checks if the value of a variable has changed (in real time) in JavaScript. It's about triggering an event when a string variable changes.

I tried:

let Variable;
let VariableMemory = Variable;
while(VariableMemory != Variable) {
 console.log("the variable has changed");
 VariableMemory = Variable;
};