HTML script injection via javascript

HTML script injection via javascript

I have a text field where user can fill href tag script which I have to
show as a link later on. But your can enter some malicious script like
alert message and more like that which will cause execution on unwanted
script at the point where I use that text field value to display. My
question is that how can I restrict user to only enter href tag releated
entry in text field and restrict other script to enter. Thanks In advance.