es6的扩展运算符，箭头函数，函数参数

1. 扩展运算符：

扩展运算符有以下四种：
        //展开数组
		let arr = [1,2,3,4];
		let a = [...arr];
		console.log(a);
			
		let b = [7,8,9,10];
		let g = [1,2,...b,4,5];
		console.log(g);
			
		//数组的拷贝
		let a = [1,2,3];
		let a1 = [...a];
		a1.push(4);
		console.log(a);
		console.log(a1);
			
		//数组的合并
		let a = [1,2,3];
		let a1 = [4,5,6];
		a = [...a,...a1];
		console.d(a);
			
		//数组的调用
		function  fn(a,b,c,d){
         	 console.log(a+b+c+d);
        	}
        	var p=[1,2,3,4,5,6];
        	let result=fn(10,...p);

2. 箭头函数：

        //箭头函数
		let a = () => {
			console.log("Hello word")
		}
		a();
		//有参数
		(name)=>{
			console.log(name);
		};
		//没有参数
		()=>{
			console.log("hi word")
		};
		d('jiang');
		//两个参数
		(name,age)=>{
			console.log(name,age);
		};
		//省略后的
		let c (a,b)=>a+b;
		(a,b)=>{console.log(a+b);
		console.log(c);
		//可以省略()
		let d = name=>{
			console.log(name);
		}
注释：箭头函数解决了定时器里的this指针问题。

3. 扩展参数(默认参数,扩展参数,剩余函数)：

//默认参数
		let sayHellow = (name,age=30)=>{
			let str = `${name} is ${age} years old`
			console.log(str);
		}
		sayHellow("songze",25);//控制台打印songze is 25 years old。
		//扩展参数
		let sum = (a,b,c) => {
			console.log(a+b+c);
		};
		let arr = [1,2,3];
		sum(...arr);//控制台打印6。
		//剩余函数
		let he = (a,b,...rest)=>{
		console.log(rest);//控制台打印[3, 4, 5, 6, 7, 8, 9]。
		console.log(a+b);//控制台打印3.
		}
		he(1,2,3,4,5,6,7,8,9);