In replace function you can see that we are passing the regular expression to replace, but if the data is dynamic and i want to replace it in runtime ?? i have to store the data in a variable and now comes the question how i can use a variable in replace function ????
suppose you are getting the value from the textbox called subject
var subject = document.getElementById('subject').value;
var main_str = "i am working as a php developer, php is favorite language ";
//i want to replace the subject variable - but as a rule in replace function we have to pass a regular exprssion
// so we cannot write main_str = main_str.replace(subject ,'JAVA'); we have to convert the subject to a regular expression
var sRegExInput = new RegExp(subject, "g");
main_str = main_str.replace(sRegExInput ,'JAVA');