String replacement---Replace the characters from the X position to the Y position

There are three ways to replace strings:

1. String connection (simple and easy to think and implement)

   Intercept a few of them, and then connect them separately.

   	var str = "asdf123456";
   	
   	var sp = function(begain, end, mainStr, replaceStr){
   	    var len = mainStr.length;
   	    end = end >= len ? len : end;
   	    begain = begain > len || begain < 0 ? 0 : begain;
   	
   	    var bStr = mainStr.substr(0, begain);
   	    var eStr = mainStr.substr(end, len);
   	    return bStr + replaceStr + eStr;
   	}
   	
   	console.log(sp(6, 10, str, "1234")); //asdf121234
   

2. The string becomes an array and then becomes a string (slightly difficult and not easy to think, but all built-in functions do not need to be implemented by yourself)

   Replace the string split into an array, then replace it with slice, and then join to return the string

   var str = "asdf123456";
   var arr = str.split('');
   var replaceArr = arr.splice(6,10, '1234');
   var res = arr.join('');
   console.log(res);
   

3. Regular (difficult but minimal code)

   var str = "asdf123456";
   var res = str.replace(/(\w{6})(\w{4})(.*)/, '$11234$3');
   console.log(res);
   

Summary: For those who are not familiar with regular rules, the second one is recommended. If you want to practice regularity, you can take a look at my notes: Portal