The script presented in this page is a JavaScript Countdown Timer that uses for the starting time data added in a form fields.
The button that starts the Countdown Timer is disabled after the user adds data for minutes /seconds in form fields, and clicks the button.
When the Countdown Timer reaches to 0, the Start button is enabled; also, you can add in the script to call a JavaScript function when minutes and seconds reach to 0 (for explanations about the code, see the comments in script).

• There is a new version of this script to this page: https://coursesweb.net/javascript/countdown-timer-starting-time-added-form

Demo (Add numeric values into the fields for minutes and seconds, then click START):
Minutes:     Seconds:
Countdown Timer:   00:00

Code for JavaScript Countdown Timer

<form>
Minutes: <input type="text" id="mns" name="mns" value="0" size="3" maxlength="3" /> &nbsp; &nbsp; Seconds: <input type="text" id="scs" name="scs" value="0" size="2" maxlength="2" /><br/>
<input type="button" id="btnct" value="START" onclick="countdownTimer()"/>
</form>
Countdown Timer: &nbsp; <span id="showmns">00</span>:<span id="showscs">00</span>
<script type="text/javascript"><!--
    /* Function to display a Countdown timer with starting time from a form */
// sets variables for minutes and seconds
var ctmnts = 0;
var ctsecs = 0;
var startchr = 0;       // used to control when to read data from form

function countdownTimer() {
  // https://coursesweb.net/javascript/
  // if $startchr is 0, and form fields exists, gets data for minutes and seconds, and sets $startchr to 1
  if(startchr == 0 && document.getElementById('mns') && document.getElementById('scs')) {
    // makes sure the script uses integer numbers
    ctmnts = parseInt(document.getElementById('mns').value) + 0;
    ctsecs = parseInt(document.getElementById('scs').value) * 1;

    // if data not a number, sets the value to 0
    if(isNaN(ctmnts)) ctmnts = 0;
    if(isNaN(ctsecs)) ctsecs = 0;

    // rewrite data in form fields to be sure that the fields for minutes and seconds contain integer number
    document.getElementById('mns').value = ctmnts;
    document.getElementById('scs').value = ctsecs;
    startchr = 1;
    document.getElementById('btnct').setAttribute('disabled', 'disabled');     // disable the button
  }

  // if minutes and seconds are 0, sets $startchr to 0, and return false
  if(ctmnts==0 && ctsecs==0) {
    startchr = 0;
    document.getElementById('btnct').removeAttribute('disabled');     // remove "disabled" to enable the button

    /* HERE YOU CAN ADD TO EXECUTE A JavaScript FUNCTION WHEN COUNTDOWN TIMER REACH TO 0 */

    return false;
  }
  else {
    // decrease seconds, and decrease minutes if seconds reach to 0
    ctsecs--;
    if(ctsecs < 0) {
      if(ctmnts > 0) {
        ctsecs = 59;
        ctmnts--;
      }
      else {
        ctsecs = 0;
        ctmnts = 0;
      }
    }
  }

  // display the time in page, and auto-calls this function after 1 seccond
  document.getElementById('showmns').innerHTML = ctmnts;
  document.getElementById('showscs').innerHTML = ctsecs;
  setTimeout('countdownTimer()', 1000);
}
//-->
</script>

Daily Test with Code Example

HTML
CSS
JavaScript
PHP-MySQL
Which tag is used to add definition lists into a <dl> element?
<dt> <dd> <li>
<dl>
 <dt>HTML</dt>
  <dd> - Hyper Text Markup Language</dd>
  <dd> - Language for web pages</dd>
</dl>
Which CSS property can hide an element on page, letting an empty space in its place?
display position visibility
#id {
  visibility: hidden;
}
Click on the event which is triggered when the mouse clicks on an object.
onclick onmouseover onfocus
document.getElementById("id").onclick = function(){
  alert("http://CoursesWeb.net/");
}
Indicate the PHP variable that contains the contents of both $_GET, $_POST, and $_COOKIE arrays.
$_SESSION $_GET $_REQUEST
if(isset($_REQUEST["id"])) {
  echo $_REQUEST["id"];
}
Countdown Timer with starting time added into a form

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