//函数参数默认值(more值后不能有参数)
{function  test(x,y = 'world'){console.log('默认值',x,y);  }test('hello');// hello worldtest('hello','kill'); //hello kill
}
//作用域概念
{let x = 'test';function test2(x,y = x){console.log('作用域',x,y);}test2(); // undefined undefinedtest2('kill');// kill killfunction test3(c,y=x){console.log('作用域',c,y);}test3();// undefined test
}//参数
{function test3(...arg){for(let v of arg){console.log('rest',v); }}test3(1,2,3,4,'a'); // 1,2,3,4,a
}//扩展运算符
{console.log(...[1,2,4]); //1,2,4console.log('a',...[1,2,4]); //a,1,2,4
}// 箭头函数
{
//函数名 参数 箭头 返回值let arrow = v => v*2;let arrow2 = () => 5;console.log('arrow',arrow(3)); //6console.log(arrow2); //function arrow2 (){ return 5};
}//伪调用
{function tail(x){console.log('tail',x); //123
    }function fx(x){return tail(x);}fx(123);
}