[Turn] The difference between substr and substring of intercepted strings

subString(start,stop)

substr(start,length)

Both substr and substring are intercepted strings. 
The two have the same point. If only one parameter is written, the function of both is the same: that is to intercept the string fragment after the current subscript of the string until the end of the string. 
E.g:

`var a=”abcdefghiklmnopqrstuvwxyz”; 
var b=a.substr(3); 
var c=a.substring(3); 
console.log(b); 
console.log(c);

In this way, the output results are the same, which are all  defghiklmnopqrstuvwxyz 
intercepted from the position where the third subscript is 2 to the end.  When writing the second parameter, the two will have completely different meanings;  substr(a,b)  The second parameter is the length of the intercepted string  substring(a, b)  The second parameter is the final subscript of the intercepted string.  For example:

var a="abcdefghiklmnopqrstuvwxyz";
var b=a.substr(3,5); var c=a.substring(3,5); 打印输出的结果是： defgh de 注意最后5下标是不会取到的意思是只能截取a字符串的3,4下标 截取的时候是不会截取到最后一个[3,5）