javascript - Fastest way to check if substring is at specific position of another string -

i have string (length 50-2000) , potential substring (length 2-8) can start @ specific position (it may occur elsewhere don't care). need test large number of strings speed key here. there faster way then:

var q = basestring.indexof(searchstring, assumedindex) === assumedindex;  

or

var q = basestring.substr(assumedindex, searchstring.length) === searchstring;  

keeping in mind amit said in comments, thought might add alternative (probably) faster @ least substr method:

var q = basestring.startswith(searchstring, assumedindex);  

from mdn:

the startswith() method determines whether string begins characters of string, returning true or false appropriate.

small example:

> "hello world!".startswith("world!",6) < true 

the reason argue may faster because polyfill (shown below) directly implemented substr, except browser implementations implemented natively , without string copying. should @ least fast suggested.

polyfill:

if (!string.prototype.startswith) {     string.prototype.startswith = function(searchstring, position){       position = position || 0;       return this.substr(position, searchstring.length) === searchstring;   }; }