To send click event to a element on plain javascript

req_script.js

function eventFire(el, etype){
  if (el.fireEvent) {
    el.fireEvent('on' + etype);
  } else {
    var evObj = document.createEvent('Events');
    evObj.initEvent(etype, true, false);
    el.dispatchEvent(evObj);
  }
}

/*
Usage:
<button id="the_id">Click Me</button>

e = document.getElementById("the_id");
eventFire(e, "click");
*/

// ========== OR ============
var elem = document.getElementById('the_id');

// Simulate clicking on the specified element.
triggerEvent( elem, 'click' );

/**
 * Trigger the specified event on the specified element.
 * @param  {Object} elem  the target element.
 * @param  {String} event the type of the event (e.g. 'click').
 */
function triggerEvent( elem, event ) {
  var clickEvent = new Event( event ); // Create the event.
  elem.dispatchEvent( clickEvent );    // Dispatch the event.
}