The engine that powers Enketo Smart Paper - Use it to develop your own enketo-powered app.
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Enketo Core npm version Build Status Dependency Status devDependency Status Codacy Badge

The engine that powers Enketo Smart Paper and various third party tools including these.

This repo is meant to use as a building block for any Enketo-powered application. See this page for a schematic overview of an Enketo-powered application and how Enketo Core fits into this.

Follow the Enketo blog or Enketo on twitter to stay up to date.

Usage as a library

  1. Install with npm install enketo-core --save or include as a git submodule.
  2. Develop a way to perform an XSL Transformation on OpenRosa-flavoured XForms inside your app. The transformation will output an XML instance and a HTML form. See enketo-transformer for an available library/app to use or develop your own.
  3. Add themes to your stylesheet build system (2 stylesheets per theme, 1 is for media="print").
  4. Override the files under "browser", e.g. using aliasify with your app-specific versions.
  5. Main methods illustrated in code below:
var Form = require('enketo-core');

// The XSL transformation result contains a HTML Form and XML instance.
// These can be obtained dynamically on the client, or at the server/
// In this example we assume the HTML was injected at the server and modelStr 
// was injected as a global variable inside a <script> tag.

// required string of the jquery selector of the HTML Form DOM element
var formSelector = 'form.or:eq(0)';

// required object containing data for the form
var data = {
  // required string of the default instance defined in the XForm
  modelStr: globalXMLInstance,
  // optional string of an existing instance to be edited
  instanceStr: null,
  // optional boolean whether this instance has ever been submitted before
  submitted: false,
  // optional array of external data objects containing: 
  // {id: 'someInstanceId', xml: xmlDocument}
  // or (NOT recommended - terrible performance for large documents):
  // {id: 'someInstanceId', xml: '<root>external instance content</root>'}
  external: [],
  // optional object of session properties 
  // 'deviceid', 'username', 'email', 'phonenumber', 'simserial', 'subscriberid'
  session: {}

// Form-specific configuration
var options = {
  clearIrrelevantImmediately: true  // this is the default, it can be omitted

// Instantiate a form, with 2 parameters
var form = new Form( formSelector, data, options);

// Initialize the form and capture any load errors
var loadErrors = form.init();

// If desired, scroll to a specific question with any XPath location expression,
// and aggregate any loadErrors.
loadErrors = loadErrors.concat( form.goTo( '//repeat[3]/node' ) );

// submit button handler for validate button
$( '#submit' ).on( 'click', function() {
  // clear irrelevant questions and validate
    .then(function (valid){
      if ( !valid ) {
        alert( 'Form contains errors. Please see fields marked in red.' );
      } else {
        // Record is valid! 
        var record = form.getDataStr();

        // reset the form view
        // reinstantiate a new form with the default model and no options
        form = new Form( formSelector, { modelStr: modelStr }, {} );

        // do what you want with the record
} );

Browser support

The following browsers are officially supported:

  • latest Android webview on latest Android OS
  • latest WKWebView on latest iOS
  • latest version of Chrome/Chromium on OS X, Linux, Windows, Android and iOS
  • latest version of Firefox on OS X, Windows, Linux, Android and iOS
  • latest version of Safari on OS X, Windows, and on the latest version of iOS
  • latest version of Microsoft Edge

We have to admit we do not test on all of these, but are committed to fixing browser-specific bugs that are reported for these browsers. Naturally, older browsers versions will often work as well - they are just not officially supported.

You can enable some support for Internet Explorer 11 by importing the _iefix.scss files where appropriate. These are commented out in the default CSS builds for the 3 themes. Also make sure to resolve the enketo/polyfills-ie11 module to /src/js/polyfills-ie11 (or an alternative polyfill service).

Global Configuration

Global configuration (per app) is done in config.json which is meant to be overriden by a config file in your own application (e.g. by using aliasify).


The maps configuration can include an array of Mapbox TileJSON objects (or a subset of these with at least a name, tiles (array) and an attribution property, and optionally maxzoom and minzoom). You can also mix and match Google Maps layers. Below is an example of a mix of two map layers provided by OSM (in TileJSON format) and Google maps.

    "name": "street",
    "tiles": [ "http://{s}{z}/{x}/{y}.png" ],
    "attribution": "Map data © <a href=\"\">OpenStreetMap</a> contributors"
    "name": "satellite",
    "tiles": "GOOGLE_SATELLITE"

For GMaps layers you have the four options as tiles values: "GOOGLE_SATELLITE", "GOOGLE_ROADMAP", "GOOGLE_HYBRID", "GOOGLE_TERRAIN". You can also add other TileJSON properties, such as minZoom, maxZoom, id to all layers.


The Google API key that is used for geolocation (in the geo widgets' search box). Can be obtained here. Make sure to enable the GeoCoding API service. If you are using Google Maps layers, the same API key is used. Make sure to enable the Google Maps JavaScript API v3 service as well in that case (see next item).


This setting with the default false value determines whether Enketo should validate questions immediately if a related value changes. E.g. if question A has a constraint that depends on question B, this mode would re-validate question A if the value for question B changes. This mode will slow down form traversal. When set to false that type of validation is only done at the end when the Submit button is clicked or in Pages mode when the user clicks Next.


This setting with default true value determines whether the Next button should trigger validation of the current page and block the user from moving to the next page if validation fails.


This setting with default true value determines whether to enable support for swiping to the next and previous page for forms that are divided into pages.

Form Configuration

Per-form configuration is done by adding an (optional) options object as 3rd parameter when instantiating a form.

Behaviour of skip logic

new Form(formselector, data, { 
  clearIrrelevantImmediately: false

If clearIrrelevantImmediately is set to true or not set at all, Enketo will clear the value of a question as soon as it becomes irrelevant, after loading (so while the user traverses the form). If it is set to false Enketo will leave the values intact (and just hide the question).

In the second case the irrelevant values will not be cleared until form.validate() is called (usually when the user marks a record as complete).

Print only the "relevant" parts of the form

If printRelevantOnly is set to true or not set at all, printing the form only includes what is visible, ie. all the groups and questions that do not have a relevant expression or for which the expression evaluates to true.

new Form(formselector, data, { 
  printRelevantOnly: false

How to develop Enketo Core

  1. install node and grunt-cli
  2. install dependencies with npm install
  3. build with grunt
  4. start built-in auto-reloading development server with npm start
  5. browse to http://localhost:8005 and load an XForm url with the xform queryparameter or load a local from from the /tests/forms folder in this repo
  6. run tests with npm test
  7. adding the querystring touch=true and reducing the window size allows you to simulate mobile touchscreens

How to create or extend widgets

To create new widgets, we recommend using this plugin template.

Each widget should fulfill the following requirements:

  • be a CommonJS jQuery plugin
  • return an object with its own name and selector-to-instantiate with
  • path to stylesheet scss file relative to the widget's own folder to be added in _widgets.scss (this will be automated in the future)
  • be responsive up to a minimum window width of 320px
  • use JSDoc style documentation
  • if hiding the original input element, it needs to load the default value from that input element into the widget
  • if hiding the original input element, it needs to stay synchronized with the widget and a change event should be triggered on the original whenever it changes value
  • if hiding the original input element, it needs to listen for the applyfocus event on the original input and focus the widget
  • if hiding the original input element, the widget value needs to update when the original input updates due to a calculation or becoming irrelevant (implement update() method)
  • it is recommended to apply the widget css class to any new elements it adds to the DOM (but not to their children)
  • new input/select/textarea elements inside widgets should have the ignore class
  • it requires the following methods (which can be automatically obtained by extending the Widget base class as demonstrated in the plugin template
    • enable() to enable the widget when a disabled ancestor gets enabled. This may be an empty function if that happens automatically.
    • disable() This may be an empty function if the widgets gets disabled automatically cross-browser when its branch becomes irrelevant.
    • update() to update the widget when called after the content used to instantiate it has changed (language, options or calculated value). In its simplest form this could simply call destroy() and then re-initialize the widget, or be an empty function if language changes are handled automatically and it is not a <select> widget.
  • if the widget needs tweaks or needs to be disabled for mobile use, use support.js to detect this.
  • allow clearing of the original input (i.e. setting value to '')
  • send a fakefocus event to the original input when the widget gets focus
  • please write test specs in the widget's /test folder.....(yeah, we need to do that for the existing widgets too...)

Notes for JavaScript Developers

  • JavaScript style see JsBeautifier config file, the jsbeautifier check is added to the grunt test task. You can also manually run grunt jsbeautifier:fix to fix style issues.
  • Testing is done with Jasmine and Karma (all: grunt karma, headless: grunt karma:headless, browsers: grunt karma:browsers)
  • When making a pull request, please add tests where relevant

Notes for CSS Developers

The core can be fairly easily extended with alternative themes. See the plain, the grid, and the formhub themes already included in /src/sass. We would be happy to discuss whether your contribution should be a part of the core, the default theme or be turned into a new theme.

For custom themes that go beyond just changing colors and fonts, keep in mind all the different contexts for a theme:

  1. non-touchscreen vs touchscreen (add ?touch=true during development)
  2. default one-page-mode and multiple-pages-mode
  3. right-to-left form language vs left-to-right form language (!) - also the UI-language may have a different directionality
  4. screen view vs. print view
  5. questions inside a (nested) repeat group have a different background
  6. large screen size --> smaller screen size ---> smallest screen size
  7. question in valid vs. invalid state


The development of this library was sponsored by:

Change log

See change log

Performance (live)

See graphs


See license document and additional clause below:

Any product that uses enketo-core is required to have a "Powered by Enketo" footer, according to the specifications below, on all screens in which enketo-core or parts thereof, are used, unless explicity exempted from this requirement by Enketo LLC in writing. Partners and sponsors of the Enketo Project, listed on and on this page are exempted from this requirements and so are contributors listed in package.json.

The aim of this requirement is to force adopters to give something back to the Enketo project, by at least spreading the word and thereby encouraging further adoption.


  1. The word "Enketo" is displayed using Enketo's logo.
  2. The minimum font-size of "Powered by" is 12 points.
  3. The minimum height of the Enketo logo matches the font-size used.
  4. The Enketo logo is hyperlinked to


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