Q:

How do i replace all dot in string to Underscore? 

I have number like 4.1.1.1 replace with 4_1_1_1
Please provide solution in jQuery. 

A:

You don't even need help here from any library, this is just plain Javascript:

var str = "4.1.1.1";
alert(str.replace(/\./g, '_'));

Read about replace method of the String prototype and also about regular expressions you can use with it.