A JavaScript function for handling the "button click" in a base converter calculator.

buttonClick.js

/*********************************************************
 * Responds to the "Convert!" button click.
 * (This could be thought of as the "main" function).
 * 
 * INPUT:         Validate the web form input.
 * PROCESSING:    Perform the conversions.
 * OUTPUT:        Display the results on the web page.
 ********************************************************/
function buttonClick() {

    // 1) Extract user data from the form fields.
    var inputNumber = document.getElementById("startField").value;
    var inputBase = document.getElementById("startBaseSelect").value;
    var outputBase = document.getElementById("endBaseSelect").value;

    // 2) Remove spaces and set letters to uppercase.
    inputNumber = sanitizeInput(inputNumber);

    // 3.1) If inputNumber and inputBase don't match, flag an error.
    if (!numberAndBaseMatch(inputNumber, inputBase)) 
      displayResult( 
        "Error: Invalid number. <br>" +
        "Please enter a positive base-" + 
        inputBase + " integer.<br>" 
      );

    // 3.2) Otherwise, proceed with the base conversion.
    else {

      // 3.2.1) Convert the inputNumber to the given outputBase.
      inputBase = parseInt(inputBase);
      outputBase = parseInt(outputBase);
      var outputNumber = baseConvert(inputNumber,inputBase,outputBase);

      // 3.2.2) Display the result on the web page.
      displayResult( 
          inputNumber + " (base " + inputBase + ") = " + 
          outputNumber + " (base " + outputBase + ")" 
      );
    }   
}