How get only a specific part of a string using a regular expression?

Question

In an input field I have the value A=123 and I need the JavaScript code to get only the 123 part.

This is what I tried so far:

 function formAnswer() { var input = document.getElementById('given').value; var match = input.match(/A=.*/); document.getElementById('result').value = match; } 

 <input type="text" id="given" placeholder="Given" value="A=123"/> <input type="text" id="result" placeholder="Result"/> <input type="button" value="Click!" onClick="formAnswer();"/> 

But this still gets the value A=123 . What am I doing wrong here?

Answer 1

Use parenthesis in your regular expression to catch what's after A= . The caught value will be available with match[1] ( match[0] will be the entire expression).

 function formAnswer() { let input = document.getElementById('given').value; match = input.match(/A=(.*)/); document.getElementById('result').value = match[1]; } 

 <input type="text" id="given" placeholder="Given"/> <input type="text" id="result" placeholder="Result"/> <input type="button" onClick="formAnswer();"/> 

Answer 2

You can try this regex: (?<=A=).*

It simply searches for a string which is preceded by "A="

 function formAnswer() { var input = document.getElementById('given').value; var match = input.match(/(?<=A=).*/); document.getElementById('result').value = match; } 

 <input type="text" id="given" placeholder="Given" value="A=123" /> <input type="text" id="result" placeholder="Result" /> <input type="button" onClick="formAnswer();" value="Check" />