（JS）状态模式

（JS）状态模式
每次状态变化都会触发逻辑
不能总是使用if…else判断

class State {
    
	constructor(color) {
    
		this.color = color;
	}
	
	handle() {
    
		console.log(`turn to ${
      this.color} light`);
		context.setState(this);
	}
}


class Context {
    
	constructor() {
    
		this.state = null;
	}
	
	getState() {
    
		return this.state;
	}
	
	setState(state) {
    
		this.state = state;
	}
}
let context = new Context();
let green = new State("green");
let red = new State("red");
let yellow = new State("yellow");
green.handle();
red.handle();
yellow.handle();
console.log(context.getState());

turn to green light
turn to red light
turn to yellow light
State {
    color: "yellow"}