How to set the hyperlink format to remain in HTML but do not implement a jump

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The teacher assigned a task, require users to log in or do not log in will have a home page (home.jsp), if the login will jump to the login screen (login.jsp), in the login screen has a verification code, but also a lot of login page like "See, change a" text, achieve click "Can't see, change a" to implement the validation code refresh. At the beginning of the index.jsp as a login.jsp to write, and then click "See not clear, for a" can realize the local refresh verification code, the code is as follows

<a href= "#" OnClick = "Checkcode ()" > Can't see Clearly, change a </a>

Because at that time index.jsp is as login.jsp, and index.jsp is the default home page of the project, so no problem, everything OK

When I built a new home.jsp, renamed Index.jsp to Login.jsp and in Web. XML to set home.jsp as the Project home page, visit login.jsp, click on the "Can't See, change a" page to jump directly to the homepage, that is, home.jsp;

Obviously, this is not the result we want; after we've referred to the 50444986 solution, everything is OK.

Here's how to modify it:

<a href= "javascript:void (null);" OnClick = "Checkcode ()" > Not clear, change a </a>

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How to set the hyperlink format to remain in HTML but do not implement a jump