How to simulate a mouse click using JavaScript?

Question

(Modified version to make it work without prototype.js)

function simulate(element, eventName)
{
    var options = extend(defaultOptions, arguments[2] || {});
    var oEvent, eventType = null;

    for (var name in eventMatchers)
    {
        if (eventMatchers[name].test(eventName)) { eventType = name; break; }
    }

    if (!eventType)
        throw new SyntaxError('Only HTMLEvents and MouseEvents interfaces are supported');

    if (document.createEvent)
    {
        oEvent = document.createEvent(eventType);
        if (eventType == 'HTMLEvents')
        {
            oEvent.initEvent(eventName, options.bubbles, options.cancelable);
        }
        else
        {
            oEvent.initMouseEvent(eventName, options.bubbles, options.cancelable, document.defaultView,
            options.button, options.pointerX, options.pointerY, options.pointerX, options.pointerY,
            options.ctrlKey, options.altKey, options.shiftKey, options.metaKey, options.button, element);
        }
        element.dispatchEvent(oEvent);
    }
    else
    {
        options.clientX = options.pointerX;
        options.clientY = options.pointerY;
        var evt = document.createEventObject();
        oEvent = extend(evt, options);
        element.fireEvent('on' + eventName, oEvent);
    }
    return element;
}

function extend(destination, source) {
    for (var property in source)
      destination[property] = source[property];
    return destination;
}

var eventMatchers = {
    'HTMLEvents': /^(?:load|unload|abort|error|select|change|submit|reset|focus|blur|resize|scroll)$/,
    'MouseEvents': /^(?:click|dblclick|mouse(?:down|up|over|move|out))$/
}
var defaultOptions = {
    pointerX: 0,
    pointerY: 0,
    button: 0,
    ctrlKey: false,
    altKey: false,
    shiftKey: false,
    metaKey: false,
    bubbles: true,
    cancelable: true
}

You can use it like this:

simulate(document.getElementById("btn"), "click");

Note that as a third parameter you can pass in 'options'. The options you don't specify are taken from the defaultOptions (see bottom of the script). So if you for example want to specify mouse coordinates you can do something like:

simulate(document.getElementById("btn"), "click", { pointerX: 123, pointerY: 321 })

You can use a similar approach to override other default options.

Credits should go to kangax. Here's the original source (prototype.js specific).

An easier and more standard way to simulate a mouse click would be directly using the event constructor to create an event and dispatch it.

Though the MouseEvent.initMouseEvent() method is kept for backward compatibility, creating of a MouseEvent object should be done using the MouseEvent() constructor.

var evt = new MouseEvent("click", {
    view: window,
    bubbles: true,
    cancelable: true,
    clientX: 20,
    /* whatever properties you want to give it */
});
targetElement.dispatchEvent(evt);

Demo: http://jsfiddle.net/DerekL/932wyok6/

This works on all modern browsers. For old browsers including IE, MouseEvent.initMouseEvent will have to be used unfortunately though it's deprecated.

var evt = document.createEvent("MouseEvents");
evt.initMouseEvent("click", canBubble, cancelable, view,
                   detail, screenX, screenY, clientX, clientY,
                   ctrlKey, altKey, shiftKey, metaKey,
                   button, relatedTarget);
targetElement.dispatchEvent(evt);

Here's a pure JavaScript function which will simulate a click (or any mouse event) on a target element:

function simulatedClick(target, options) {

  var event = target.ownerDocument.createEvent('MouseEvents'),
      options = options || {},
      opts = { // These are the default values, set up for un-modified left clicks
        type: 'click',
        canBubble: true,
        cancelable: true,
        view: target.ownerDocument.defaultView,
        detail: 1,
        screenX: 0, //The coordinates within the entire page
        screenY: 0,
        clientX: 0, //The coordinates within the viewport
        clientY: 0,
        ctrlKey: false,
        altKey: false,
        shiftKey: false,
        metaKey: false, //I *think* 'meta' is 'Cmd/Apple' on Mac, and 'Windows key' on Win. Not sure, though!
        button: 0, //0 = left, 1 = middle, 2 = right
        relatedTarget: null,
      };

  //Merge the options with the defaults
  for (var key in options) {
    if (options.hasOwnProperty(key)) {
      opts[key] = options[key];
    }
  }

  //Pass in the options
  event.initMouseEvent(
      opts.type,
      opts.canBubble,
      opts.cancelable,
      opts.view,
      opts.detail,
      opts.screenX,
      opts.screenY,
      opts.clientX,
      opts.clientY,
      opts.ctrlKey,
      opts.altKey,
      opts.shiftKey,
      opts.metaKey,
      opts.button,
      opts.relatedTarget
  );

  //Fire the event
  target.dispatchEvent(event);
}

Here's a working example: http://www.spookandpuff.com/examples/clickSimulation.html

You can simulate a click on any element in the DOM. Something like simulatedClick(document.getElementById('yourButtonId')) would work.

You can pass in an object into options to override the defaults (to simulate which mouse button you want, whether Shift/Alt/Ctrl are held, etc. The options it accepts are based on the MouseEvents API.

I've tested in Firefox, Safari and Chrome. Internet Explorer might need special treatment, I'm not sure.

From the Mozilla Developer Network (MDN) documentation, HTMLElement.click() is what you're looking for. You can find out more events here.

Based on Derek's answer, I verified that

document.getElementById('testTarget')
  .dispatchEvent(new MouseEvent('click', {shiftKey: true}))

works as expected even with key modifiers. And this is not a deprecated API, as far as I can see. You can verify on this page as well.

You can use elementFromPoint:

document.elementFromPoint(x, y);

supported in all browsers: https://caniuse.com/#feat=element-from-point