1.都为正整数//例子数据
var arr = [1,2,3,4,5,6,7],
var str = "helloworld!";  //注意这里有个！号也算一位若有空格，空格也算一位

console.log(str.slice(1));  //elloworld!
console.log(str.substring(1)); //elloworld!
console.log(str.substr(1));  //elloworld! 

console.log(arr.slice(1));  //[2,3,4,5,6,7]
console.log(arr.substr(1));  //TypeError: arr.substr is not a function
console.log(arr.substring(1));  //TypeError: arr.substring is not a function

数组是没有substr和substring方法的，含str的都是字符串专用

//例子不变
console.log(str.slice(1,4));  //ell 不包含结束位1起始位，4结束位
console.log(str.substring(1,4));  //ell 不包含结束位1起始位，4结束位
console.log(str.substr(1,4)); //ello  不一致了！！！ console.log(arr.slice(1,4)); //[2,3,4]  不包含结束位1起始位，4结束位

3. 都使用两个正数参数（第一个大于第二个）：
var arr = [1,2,3,4,5,6,7],
var  str = "helloworld!";
console.log(str.slice(5,1));  //""
console.log(str.substring(5,1));  //ello
console.log(str.substr(5,1));  //"w"console.log(arr.slice(5,1));  //[]

var arr = [1,2,3,4,5,6,7],
var str = "helloworld!";
console.log(str.slice(1,-2)); //elloworl
console.log(str.substr(1,-2));  //""
console.log(str.substring(1,-2));  //hconsole.log(arr.slice(1,-2)); //[ 2, 3, 4, 5]

//例子不变
console.log(str.slice(-3,1))  //""
console.log(str.substr(-3,1))  //l
console.log(str.substring(-3,1))  //h

console.log(arr.slice(-3,1))  //[]

//例子不变
console.log(str.slice(-1,-5));
console.log(str.substr(-1,-5));
console.log(str.substring(-1,-5));console.log(arr.slice(-1,-5));
//上面的结果全是空

console.log(str.slice(-5,-1)); //orld
console.log(str.substr(-5,-1)); //""
console.log(str.substring(-5,-1)); //""

console.log(arr.slice(-5,-1)); //[ 3, 4, 5, 6 ]