Optimizely Web Experimentation uses some common functions to deliver experiences. You can also use those functions to write your own custom experiences.

Syntax

utils = window["optimizely"].get("utils");

Parameters

Parameter and Type	Child Attribute	Description
utils string	N/A	The argument indicating to get the utils object. Required.

Return value

Parameter and type	Child attribute	Description
UtilsObject	N/A	The utils object that contains a number of useful functions for developing experiences.
observeSelector function[observeSelector]	Child attribute of type `UtilsObject`.	Run a callback whenever an element changes.
poll function[poll]	Child attribute of type `UtilsObject`.	A `setInterval` wrapper.
waitUntil function[waitUntil]	Child attribute of type `UtilsObject`.	Wait until the provided function returns true.
waitForElement function[waitForElement]	Child attribute of type `UtilsObject`.	Returns a Promise that is resolved with the first HTMLDomElement that matches the supplied selector.
onUrlChange function[onUrlChange]	Child attribute of type `UtilsObject`.	Run a callback whenever the URL of the current page changes.
persistHtml function[persistHtml]	Child attribute of type `UtilsObject`.	Injects HTML onto the page and re-injects the HTML if it is ever removed.

Example call

utils = window["optimizely"].get("utils");

Example return value

utils.waitForElement(selector);
utils.observeSelector(selector, callback, options);
utils.poll(callback, delay);
utils.waitUntil(conditionFn);
utils.onUrlChange(callback);
utils.persistHtml(html, selector, position);

waitForElement()

Returns a Promise that is resolved with the first HTMLDomElement that matches the supplied selector. This is commonly used to make adjustments to the element that you are waiting for when the promise is fulfilled.

Syntax

utils.waitForElement(selector);

Parameters

Parameter and Type	Child Attribute	Description
selector string	N/A	A CSS selector indicating the element to wait for. Required.

Return value

Parameter and type	Child attribute	Description
Promise	N/A	An ES6-style Promise that is resolved with the matching element.

Example call

utils.waitForElement("h2");

Examples

Change the color of an element

Wait for an element to be loaded on the dom and change the color as soon as it has become available.

Example code for changing the color of an element

// Retrieve the utils library
var utils = window["optimizely"].get('utils');

// Wait for the footer element to appear in the DOM, then change the color
utils.waitForElement('.footer').then(function(footerElement) {
  footerElement.style.color = 'black';
});

observeSelector()

Run a callback whenever an element changes. This utility provides a subset of the functionality of a MutationObserver, letting you run a function whenever a DOM selector changes. Given a CSS selector and a callback, this function invokes the supplied callback whenever a new element appears in the DOM matching the supplied selector.

Syntax

utils.observeSelector(selector, callback, options);

Parameters

Parameter and type	Child attribute	Description
selector string	N/A	A CSS selector indicating the element to wait for. Required.
callback function	N/A	The function that will be executed when the element indicated by the selector changes. The first argument is the exact element that changed. Required.
options ObserverOptions	N/A	Timing configuration options. Required.
timeout integer or null	Child attribute of type `ObserverOptions`.	Number of milliseconds or null. Default to null (for example, no timeout).
once Boolean	Child attribute of type `ObserverOptions`.	Only invoke the callback on the first match.
onTimeout function	Child attribute of type `ObserverOptions`.	If timeout is specified and no elements match, execute timeout callback.

Return value

Parameter and type	Child attribute	Description
function	N/A	A function that can be executed to `unobserve` selector.

Example call

utils.observeSelector(".productPrice", function(priceElement) {
  priceElement.style.fontSize = '30px';
  priceElement.style.color = 'red';
}, {
  "timeout": 6000,
  "once": true,
  "onTimeout": function() {
    console.log("Stopped observing");
  }
});

poll()

A setInterval wrapper. The poll function is a convenient wrapper around the setInterval function.

Syntax

utils.poll(callback, delay);

Parameters and Types

Parameter and type	Child attribute	Description
callback function	N/A	Function to be executed on the interval specified by `delay`. Required.
delay integer	N/A	Milliseconds to wait in between each callback invocation. Required.

Return value

Parameter and Type	Child Attribute	Description
function	N/A	Returns a function that cancels the polling.

Example call

var utils = window["optimizely"].get("utils");

var cancelPolling = utils.poll(function() {
  timeRemaining = timeRemaining - 1000;

  // Update message based on how much time is remaining
  if (timeRemaining > 0) {
    var date = new Date(timeRemaining);
    headerElement.innerHTML = 'You have ' + date.getMinutes() + ':' + date.getSeconds() + ' before your reservation expires.';
  } else {
    headerElement.innerHTML = 'Your reservation has expired';
    cancelPolling();
  }
}, 1000);

waitUntil()

Wait until the provided function returns true. This utility accepts a function that returns a Boolean value and returns a Promise that resolves when the supplied function returns true.

Syntax

utils.waitUntil(conditionFunction);

Parameters

Parameter and Type	Child Attribute	Description
conditionFunction function	N/A	A function that executes synchronously and returns a truthy value when the condition is met. Required.

Return value

Parameter and type	Child attribute	Description
Promise	N/A	An ES6-style Promise that is resolved with the matching element.

Example call

utils.waitUntil(function() {
  var productsShownOnThePage = document.querySelectorAll('.product-listing');
  return productsShownOnThePage && productsShownOnThePage.length > 200;
});

onUrlChange()

Runs a callback whenever the current URL changes. This utility provides a subset of the functionality of an Event Listener, letting you run a function whenever the current URL changes. This is useful for re-applying changes on a dynamic website where the page does not fully reload during page navigation.

Syntax

utils.onUrlChange(callback);

Parameters

Parameter and Type	Child Attribute	Description
callback function	N/A	The function that executes when the URL loaded in the browser change (without a full page reload). Required.

Return value

Parameter and type	Child attribute	Description
Promise	N/A	A function that can be executed to stop the `observer` from watching for URL changes.

Example call

utils.onUrlChange(function() {
  // Ensure navigation bar stays blue during page navigation 
  document.querySelectorAll('.nav').style.color = 'blue';
});

persistHtml()

Persist a block of HTML on the page. This utility provides a subset of the functionality of a MutationObserver, letting you re-insert and persist HTML onto a page if it is removed. Given a CSS selector and position, this function places the supplied HTML at the position specified around the element in the DOM matching the supplied selector. This is useful for persisting HTML changes on a dynamic website that may remove or 're-hydrate' during page navigation.

Syntax

utils.persistHtml(html, selector, placement);

Parameters

Parameter and type	Child attribute	Description
html string	N/A	A string representation of HTML code to be added to and persisted on the page. Required.
selector string	N/A	A CSS selector indicating the element the HTML should be inserted around. Required.
placement string	N/A	The position around the `selector` to insert the `html`. Accepted values are `before`, `after`, `afterbegin`, `beforeend` Default value is `before`.

Return value

Parameter and type	Child attribute	Description
Promise	N/A	A function that removes the HTML from the page and stops further injection.

Example call

// Insert and persist a butter bar before the .nav element
const butterBarHtml = `<div class='butterBar'>This is a notification </div>`
utils.persistHtml(butterBarHtml, '.nav', 'before');

Examples

Warn after scrolling

Show the visitor an alert after the visitor has scrolled a significant distance down the page.

// Retrieve the utils library
var utils = window["optimizely"].get('utils');

// We have infinite scroll enabled on the site. Wait until more than 200 products have been shown
// to prompt the user to try out our filter by color feature
utils.waitUntil(function() {
  var productsShownOnThePage = document.querySelectorAll('.product-listing');
  return productsShownOnThePage && productsShownOnThePage.length > 200;
}).then(function() {
  alert('Not finding what you are looking for? Try narrowing down your search using our new filter by color feature');
});

For usage patterns that combine utils.waitUntil and utils.waitForElement with page activation, see Use utility functions on dynamic pages.