OOP & Classes in JavaScript - Exercise 3
A static method belongs to the class itself rather than to individual instances.
class MathTools {
static double(value) { return value * 2; }
}
console.log(MathTools.double(4));Use the static keyword for data shared by the class rather than stored on each instance.
class User {
static role = 'member';
}
console.log(User.role);Composition combines focused capabilities without creating a rigid parent-child hierarchy.
const canLog = (object) => ({
log(message) { console.log(message); return object; }
});
const service = canLog({ name: 'Orders' });Keep state private and expose methods that validate every update.
class Progress {
#value = 0;
advance(step) {
this.#value = Math.min(100, Math.max(0, this.#value + step));
}
get value() { return this.#value; }
}It assigns an initial value directly in the class body before the constructor continues.
class Cart {
items = [];
currency = 'USD';
add(item) { this.items.push(item); }
}Use an arrow-function field or bind the method when passing it as a callback.
class Timer {
seconds = 0;
tick = () => { this.seconds += 1; };
}
setInterval(new Timer().tick, 1000);Keep responsibilities focused, document the public contract, and avoid exposing mutable internal state.
class Repository {
findById(id) { return this.records.find(record => record.id === id); }
constructor(records = []) { this.records = [...records]; }
}Use the simplest abstraction that fits. A plain object or function is often clearer when there is no shared lifecycle, identity, or behavior to model.
function formatPrice(amount, currency = 'USD') {
return new Intl.NumberFormat('en', { style: 'currency', currency }).format(amount);
}A class expression creates a class as part of an expression, making it useful when a class needs to be assigned or passed as a value.
const Counter = class {
value = 0;
increment() { this.value++; }
};
const counter = new Counter();Validate constructor arguments and updates at the class boundary so instances cannot enter invalid states.
class Score {
#value = 0;
add(points) {
if (points < 0) throw new Error('Points must be positive');
this.#value += points;
}
}