Question

I am trying to get a value from input field.

I want to check if the string has % or * at the beginning of the string then show an alert.

Answer 1

if (/^[%*]/.test(document.getElementById("yourelementid").value))
   alert("Where can I find a JavaScript tutorial?");

By way of explanation: the regular expression /^[%*]/ means:

^       match the beginning of the string, followed immediately by
[%*]    any one of the characters inside the brackets

Testing the entered value against that regex will return true or false.