163. EventEmitter 实现
class EventEmitter {
constructor() {
this.events = {};
}
on(event, callback) {
let callbacks = this.events[event] || [];
callbacks.push(callback);
this.events[event] = callbacks;
return this;
}
off(event, callback) {
let callbacks = this.events[event];
this.events[event] = callbacks && callbacks.filter((fn) => fn !== callback);
return this;
}
emit(event, ...args) {
let callbacks = this.events[event];
callbacks.forEach((fn) => {
fn(...args);
});
return this;
}
once(event, callback) {
let wrapFun = (...args) => {
callback(...args);
this.off(event, wrapFun);
};
this.on(event, wrapFun);
return this;
}
}