How to clear text field on focus of text field

Question

I want to clear the text field when the user clicks on that

Answer 1

This is how I use it for a temperature converter/calculator - when the user types (keyup), the text input box calculates using the assigned function; when the user selects the other text input (there are only two inputs), the selected text input will clear.

HTML:

Input:
    


  


  
Result:


    
  
  

JavaScript:

function Conversion() {
    var tempCels = parseFloat(document.getElementById('celsius').value);
      tempFarh =(tempCels)*(1.8)+(32);
      document.getElementById('fahrenheit').value= tempFarh;
 }

function Conversion2() {
    var tempFarh = parseFloat(document.getElementById('fahrenheit').value);
      tempCels =(tempFarh - 32)/(1.8);
      document.getElementById('celsius').value= tempCels;
 }