js中substring、slice与substr的区别有哪些？

var test = 'hello world';

alert(test.slice(-3));         //rld

alert(test.substring(-3));     //hello world

alert(test.substr(-3));        //rld

alert(test.slice(3,-4));       //lo w

alert(test.substring(3,-4));   //hel

alert(test.substr(3,-4));      //空字符串