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/* modified to be compatible with browserify */
var ko = require('knockout');
var WM = require('weakmap');
* Knockout ES5 plugin -
* Copyright (c) Steve Sanderson
* MIT license
var global = this;
'use strict';
// Model tracking
// --------------
// This is the central feature of Knockout-ES5. We augment model objects by converting properties
// into ES5 getter/setter pairs that read/write an underlying Knockout observable. This means you can
// use plain JavaScript syntax to read/write the property while still getting the full benefits of
// Knockout's automatic dependency detection and notification triggering.
// For comparison, here's Knockout ES3-compatible syntax:
// var firstNameLength = myModel.user().firstName().length; // Read
// myModel.user().firstName('Bert'); // Write
// ... versus Knockout-ES5 syntax:
// var firstNameLength = myModel.user.firstName.length; // Read
// myModel.user.firstName = 'Bert'; // Write
// `ko.track(model)` converts each property on the given model object into a getter/setter pair that
// wraps a Knockout observable. Optionally specify an array of property names to wrap; otherwise we
// wrap all properties. If any of the properties are already observables, we replace them with
// ES5 getter/setter pairs that wrap your original observable instances. In the case of readonly
// ko.computed properties, we simply do not define a setter (so attempted writes will be ignored,
// which is how ES5 readonly properties normally behave).
// By design, this does *not* recursively walk child object properties, because making literally
// everything everywhere independently observable is usually unhelpful. When you do want to track
// child object properties independently, define your own class for those child objects and put
// a separate ko.track call into its constructor --- this gives you far more control.
function track(obj, propertyNames) {
if (!obj || typeof obj !== 'object') {
throw new Error('When calling ko.track, you must pass an object as the first parameter.');
var allObservablesForObject = getAllObservablesForObject(obj, true);
propertyNames = propertyNames || Object.getOwnPropertyNames(obj);
propertyNames.forEach(function(propertyName) {
// Skip properties that are already tracked
if (propertyName in allObservablesForObject) {
// Skip properties where descriptor can't be redefined
if ( false === Object.getOwnPropertyDescriptor(obj, propertyName).configurable ){
var origValue = obj[propertyName],
isArray = Array.isArray(origValue),
observable = ko.isObservable(origValue) ? origValue
: isArray ? ko.observableArray(origValue)
: ko.observable(origValue);
Object.defineProperty(obj, propertyName, {
configurable: true,
enumerable: true,
get: observable,
set: ko.isWriteableObservable(observable) ? observable : undefined
allObservablesForObject[propertyName] = observable;
if (isArray) {
notifyWhenPresentOrFutureArrayValuesMutate(ko, observable);
return obj;
// Lazily created by `getAllObservablesForObject` below. Has to be created lazily because the
// WeakMap factory isn't available until the module has finished loading (may be async).
var objectToObservableMap;
// Gets or creates the hidden internal key-value collection of observables corresponding to
// properties on the model object.
function getAllObservablesForObject(obj, createIfNotDefined) {
if (!objectToObservableMap) {
objectToObservableMap = weakMapFactory();
var result = objectToObservableMap.get(obj);
if (!result && createIfNotDefined) {
result = {};
objectToObservableMap.set(obj, result);
return result;
// Removes the internal references to observables mapped to the specified properties
// or the entire object reference if no properties are passed in. This allows the
// observables to be replaced and tracked again.
function untrack(obj, propertyNames) {
if (!objectToObservableMap) {
if (arguments.length === 1) {
} else {
var allObservablesForObject = getAllObservablesForObject(obj, false);
if (allObservablesForObject) {
propertyNames.forEach(function(propertyName) {
delete allObservablesForObject[propertyName];
// Computed properties
// -------------------
// The preceding code is already sufficient to upgrade ko.computed model properties to ES5
// getter/setter pairs (or in the case of readonly ko.computed properties, just a getter).
// These then behave like a regular property with a getter function, except they are smarter:
// your evaluator is only invoked when one of its dependencies changes. The result is cached
// and used for all evaluations until the next time a dependency changes).
// However, instead of forcing developers to declare a ko.computed property explicitly, it's
// nice to offer a utility function that declares a computed getter directly.
// Implements `ko.defineProperty`
function defineComputedProperty(obj, propertyName, evaluatorOrOptions) {
var ko = this,
computedOptions = { owner: obj, deferEvaluation: true };
if (typeof evaluatorOrOptions === 'function') { = evaluatorOrOptions;
} else {
if ('value' in evaluatorOrOptions) {
throw new Error('For ko.defineProperty, you must not specify a "value" for the property. ' +
'You must provide a "get" function.');
if (typeof evaluatorOrOptions.get !== 'function') {
throw new Error('For ko.defineProperty, the third parameter must be either an evaluator function, ' +
'or an options object containing a function called "get".');
} = evaluatorOrOptions.get;
computedOptions.write = evaluatorOrOptions.set;
obj[propertyName] = ko.computed(computedOptions);, obj, [propertyName]);
return obj;
// Array handling
// --------------
// Arrays are special, because unlike other property types, they have standard mutator functions
// (`push`/`pop`/`splice`/etc.) and it's desirable to trigger a change notification whenever one of
// those mutator functions is invoked.
// Traditionally, Knockout handles this by putting special versions of `push`/`pop`/etc. on observable
// arrays that mutate the underlying array and then trigger a notification. That approach doesn't
// work for Knockout-ES5 because properties now return the underlying arrays, so the mutator runs
// in the context of the underlying array, not any particular observable:
// // Operates on the underlying array value
// myModel.someCollection.push('New value');
// To solve this, Knockout-ES5 detects array values, and modifies them as follows:
// 1. Associates a hidden subscribable with each array instance that it encounters
// 2. Intercepts standard mutators (`push`/`pop`/etc.) and makes them trigger the subscribable
// Then, for model properties whose values are arrays, the property's underlying observable
// subscribes to the array subscribable, so it can trigger a change notification after mutation.
// Given an observable that underlies a model property, watch for any array value that might
// be assigned as the property value, and hook into its change events
function notifyWhenPresentOrFutureArrayValuesMutate(ko, observable) {
var watchingArraySubscription = null;
ko.computed(function () {
// Unsubscribe to any earlier array instance
if (watchingArraySubscription) {
watchingArraySubscription = null;
// Subscribe to the new array instance
var newArrayInstance = observable();
if (newArrayInstance instanceof Array) {
watchingArraySubscription = startWatchingArrayInstance(ko, observable, newArrayInstance);
// Listens for array mutations, and when they happen, cause the observable to fire notifications.
// This is used to make model properties of type array fire notifications when the array changes.
// Returns a subscribable that can later be disposed.
function startWatchingArrayInstance(ko, observable, arrayInstance) {
var subscribable = getSubscribableForArray(ko, arrayInstance);
return subscribable.subscribe(observable);
// Lazily created by `getSubscribableForArray` below. Has to be created lazily because the
// WeakMap factory isn't available until the module has finished loading (may be async).
var arraySubscribablesMap;
// Gets or creates a subscribable that fires after each array mutation
function getSubscribableForArray(ko, arrayInstance) {
if (!arraySubscribablesMap) {
arraySubscribablesMap = weakMapFactory();
var subscribable = arraySubscribablesMap.get(arrayInstance);
if (!subscribable) {
subscribable = new ko.subscribable();
arraySubscribablesMap.set(arrayInstance, subscribable);
var notificationPauseSignal = {};
wrapStandardArrayMutators(arrayInstance, subscribable, notificationPauseSignal);
addKnockoutArrayMutators(ko, arrayInstance, subscribable, notificationPauseSignal);
return subscribable;
// After each array mutation, fires a notification on the given subscribable
function wrapStandardArrayMutators(arrayInstance, subscribable, notificationPauseSignal) {
['pop', 'push', 'reverse', 'shift', 'sort', 'splice', 'unshift'].forEach(function(fnName) {
var origMutator = arrayInstance[fnName];
arrayInstance[fnName] = function() {
var result = origMutator.apply(this, arguments);
if (notificationPauseSignal.pause !== true) {
return result;
// Adds Knockout's additional array mutation functions to the array
function addKnockoutArrayMutators(ko, arrayInstance, subscribable, notificationPauseSignal) {
['remove', 'removeAll', 'destroy', 'destroyAll', 'replace'].forEach(function(fnName) {
// Make it a non-enumerable property for consistency with standard Array functions
Object.defineProperty(arrayInstance, fnName, {
enumerable: false,
value: function() {
var result;
// These additional array mutators are built using the underlying push/pop/etc.
// mutators, which are wrapped to trigger notifications. But we don't want to
// trigger multiple notifications, so pause the push/pop/etc. wrappers and
// delivery only one notification at the end of the process.
notificationPauseSignal.pause = true;
try {
// Creates a temporary observableArray that can perform the operation.
result = ko.observableArray.fn[fnName].apply(ko.observableArray(arrayInstance), arguments);
finally {
notificationPauseSignal.pause = false;
return result;
// Static utility functions
// ------------------------
// Since Knockout-ES5 sets up properties that return values, not observables, you can't
// trivially subscribe to the underlying observables (e.g., `someProperty.subscribe(...)`),
// or tell them that object values have mutated, etc. To handle this, we set up some
// extra utility functions that can return or work with the underlying observables.
// Returns the underlying observable associated with a model property (or `null` if the
// model or property doesn't exist, or isn't associated with an observable). This means
// you can subscribe to the property, e.g.:
// ko.getObservable(model, 'propertyName')
// .subscribe(function(newValue) { ... });
function getObservable(obj, propertyName) {
if (!obj || typeof obj !== 'object') {
return null;
var allObservablesForObject = getAllObservablesForObject(obj, false);
return (allObservablesForObject && allObservablesForObject[propertyName]) || null;
// Causes a property's associated observable to fire a change notification. Useful when
// the property value is a complex object and you've modified a child property.
function valueHasMutated(obj, propertyName) {
var observable = getObservable(obj, propertyName);
if (observable) {
// Module initialisation
// ---------------------
// When this script is first evaluated, it works out what kind of module loading scenario
// it is in (Node.js or a browser `<script>` tag), stashes a reference to its dependencies
// (currently that's just the WeakMap shim), and then finally attaches itself to whichever
// instance of Knockout.js it can find.
// A function that returns a new ES6-compatible WeakMap instance (using ES5 shim if needed).
// Instantiated by prepareExports, accounting for which module loader is being used.
var weakMapFactory;
// Extends a Knockout instance with Knockout-ES5 functionality
function attachToKo(ko) {
ko.track = track;
ko.untrack = untrack;
ko.getObservable = getObservable;
ko.valueHasMutated = valueHasMutated;
ko.defineProperty = defineComputedProperty;
// Determines which module loading scenario we're in, grabs dependencies, and attaches to KO
function prepareExports() {
// Node.js case - load KO and WeakMap modules synchronously
weakMapFactory = function() { return new WM(); };
module.exports = ko;
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