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observable-slim.js
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observable-slim.js
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/*
* Observable Slim
* Version 0.1.6
* https://github.com/elliotnb/observable-slim
*
* Licensed under the MIT license:
* http://www.opensource.org/licenses/MIT
*
* Observable Slim is a singleton that allows you to observe changes made to an object and any nested
* children of that object. It is intended to assist with one-way data binding, that is, in MVC parlance,
* reflecting changes in the model to the view. Observable Slim aspires to be as lightweight and easily
* understood as possible. Minifies down to roughly 3000 characters.
*/
var ObservableSlim = (function() {
var paths = [];
// An array that stores all of the observables created through the public create() method below.
var observables = [];
// An array of all the objects that we have assigned Proxies to
var targets = [];
// An array of arrays containing the Proxies created for each target object. targetsProxy is index-matched with
// 'targets' -- together, the pair offer a Hash table where the key is not a string nor number, but the actual target object
var targetsProxy = [];
// this variable tracks duplicate proxies assigned to the same target.
// the 'set' handler below will trigger the same change on all other Proxies tracking the same target.
// however, in order to avoid an infinite loop of Proxies triggering and re-triggering one another, we use dupProxy
// to track that a given Proxy was modified from the 'set' handler
var dupProxy = null;
var _getProperty = function(obj, path) {
return path.split('.').reduce(function(prev, curr) {
return prev ? prev[curr] : undefined
}, obj || self)
};
/**
* Create a new ES6 `Proxy` whose changes we can observe through the `observe()` method.
* @param {object} target Plain object that we want to observe for changes.
* @param {boolean|number} domDelay If `true`, then the observed changes to `target` will be batched up on a 10ms delay (via `setTimeout()`).
* If `false`, then the `observer` function will be immediately invoked after each individual change made to `target`. It is helpful to set
* `domDelay` to `true` when your `observer` function makes DOM manipulations (fewer DOM redraws means better performance). If a number greater
* than zero, then it defines the DOM delay in milliseconds.
* @param {function(ObservableSlimChange[])} [observer] Function that will be invoked when a change is made to the proxy of `target`.
* When invoked, this function is passed a single argument: an array of `ObservableSlimChange` detailing each change that has been made.
* @param {object} originalObservable The original observable created by the user, exists for recursion purposes, allows one observable to observe
* change on any nested/child objects.
* @param {{target: object, property: string}[]} originalPath Array of objects, each object having the properties `target` and `property`:
* `target` is referring to the observed object itself and `property` referring to the name of that object in the nested structure.
* The path of the property in relation to the target on the original observable, exists for recursion purposes, allows one observable to observe
* change on any nested/child objects.
* @returns {ProxyConstructor} Proxy of the target object.
*/
var _create = function(target, domDelay, originalObservable, originalPath) {
var observable = originalObservable || null;
// record the nested path taken to access this object -- if there was no path then we provide the first empty entry
var path = originalPath || [{"target":target,"property":""}];
paths.push(path);
// in order to accurately report the "previous value" of the "length" property on an Array
// we must use a helper property because intercepting a length change is not always possible as of 8/13/2018 in
// Chrome -- the new `length` value is already set by the time the `set` handler is invoked
if (target instanceof Array) {
if (!target.hasOwnProperty("__length"))
Object.defineProperty(target, "__length", { enumerable: false, value: target.length, writable: true });
else
target.__length = target.length;
}
var changes = [];
/**
* Returns a string of the nested path (in relation to the top-level observed object) of the property being modified or deleted.
* @param {object} target Plain object that we want to observe for changes.
* @param {string} property Property name.
* @param {boolean} [jsonPointer] Set to `true` if the string path should be formatted as a JSON pointer rather than with the dot notation
* (`false` as default).
* @returns {string} Nested path (e.g., `hello.testing.1.bar` or, if JSON pointer, `/hello/testing/1/bar`).
*/
var _getPath = function(target, property, jsonPointer) {
var fullPath = "";
var lastTarget = null;
// loop over each item in the path and append it to full path
for (var i = 0; i < path.length; i++) {
// if the current object was a member of an array, it's possible that the array was at one point
// mutated and would cause the position of the current object in that array to change. we perform an indexOf
// lookup here to determine the current position of that object in the array before we add it to fullPath
if (lastTarget instanceof Array && !isNaN(path[i].property)) {
path[i].property = lastTarget.indexOf(path[i].target);
}
fullPath = fullPath + "." + path[i].property
lastTarget = path[i].target;
}
// add the current property
fullPath = fullPath + "." + property;
// remove the beginning two dots -- ..foo.bar becomes foo.bar (the first item in the nested chain doesn't have a property name)
fullPath = fullPath.substring(2);
if (jsonPointer === true) fullPath = "/" + fullPath.replace(/\./g, "/");
return fullPath;
};
var _notifyObservers = function(numChanges) {
// if the observable is paused, then we don't want to execute any of the observer functions
if (observable.paused === true) return;
var domDelayIsNumber = typeof domDelay === 'number';
// execute observer functions on a 10ms setTimeout, this prevents the observer functions from being executed
// separately on every change -- this is necessary because the observer functions will often trigger UI updates
if (domDelayIsNumber || domDelay === true) {
setTimeout(function() {
if (numChanges === changes.length) {
// we create a copy of changes before passing it to the observer functions because even if the observer function
// throws an error, we still need to ensure that changes is reset to an empty array so that old changes don't persist
var changesCopy = changes.slice(0);
changes = [];
// invoke any functions that are observing changes
for (var i = 0; i < observable.observers.length; i++) observable.observers[i](changesCopy);
}
}, (domDelayIsNumber && domDelay > 0) ? domDelay : 10);
} else {
// we create a copy of changes before passing it to the observer functions because even if the observer function
// throws an error, we still need to ensure that changes is reset to an empty array so that old changes don't persist
var changesCopy = changes.slice(0);
changes = [];
// invoke any functions that are observing changes
for (var i = 0; i < observable.observers.length; i++) observable.observers[i](changesCopy);
}
};
var handler = {
get: function(target, property) {
// implement a simple check for whether or not the object is a proxy, this helps the .create() method avoid
// creating Proxies of Proxies.
if (property === "__getTarget") {
return target;
} else if (property === "__isProxy") {
return true;
// from the perspective of a given observable on a parent object, return the parent object of the given nested object
} else if (property === "__getParent") {
return function(i) {
if (typeof i === "undefined") var i = 1;
var parentPath = _getPath(target, "__getParent").split(".");
parentPath.splice(-(i+1),(i+1));
return _getProperty(observable.parentProxy, parentPath.join("."));
}
// return the full path of the current object relative to the parent observable
} else if (property === "__getPath") {
// strip off the 12 characters for ".__getParent"
var parentPath = _getPath(target, "__getParent");
return parentPath.slice(0, -12);
}
// for performance improvements, we assign this to a variable so we do not have to lookup the property value again
var targetProp = target[property];
if (target instanceof Date && targetProp instanceof Function && targetProp !== null) {
return targetProp.bind(target);
}
// if we are traversing into a new object, then we want to record path to that object and return a new observable.
// recursively returning a new observable allows us a single Observable.observe() to monitor all changes on
// the target object and any objects nested within.
if (targetProp instanceof Object && targetProp !== null && target.hasOwnProperty(property)) {
// if we've found a proxy nested on the object, then we want to retrieve the original object behind that proxy
if (targetProp.__isProxy === true) targetProp = targetProp.__getTarget;
// if the object accessed by the user (targetProp) already has a __targetPosition AND the object
// stored at target[targetProp.__targetPosition] is not null, then that means we are already observing this object
// we might be able to return a proxy that we've already created for the object
if (targetProp.__targetPosition > -1 && targets[targetProp.__targetPosition] !== null) {
// loop over the proxies that we've created for this object
var ttp = targetsProxy[targetProp.__targetPosition];
for (var i = 0, l = ttp.length; i < l; i++) {
// if we find a proxy that was setup for this particular observable, then return that proxy
if (observable === ttp[i].observable) {
return ttp[i].proxy;
}
}
}
// if we're arrived here, then that means there is no proxy for the object the user just accessed, so we
// have to create a new proxy for it
// create a shallow copy of the path array -- if we didn't create a shallow copy then all nested objects would share the same path array and the path wouldn't be accurate
var newPath = path.slice(0);
newPath.push({"target":targetProp,"property":property});
return _create(targetProp, domDelay, observable, newPath);
} else {
return targetProp;
}
},
deleteProperty: function(target, property) {
// was this change an original change or was it a change that was re-triggered below
var originalChange = true;
if (dupProxy === proxy) {
originalChange = false;
dupProxy = null;
}
// in order to report what the previous value was, we must make a copy of it before it is deleted
var previousValue = Object.assign({}, target);
// record the deletion that just took place
changes.push({
"type":"delete"
,"target":target
,"property":property
,"newValue":null
,"previousValue":previousValue[property]
,"currentPath":_getPath(target, property)
,"jsonPointer":_getPath(target, property, true)
,"proxy":proxy
});
if (originalChange === true) {
// perform the delete that we've trapped if changes are not paused for this observable
if (!observable.changesPaused) delete target[property];
for (var a = 0, l = targets.length; a < l; a++) if (target === targets[a]) break;
// loop over each proxy and see if the target for this change has any other proxies
var currentTargetProxy = targetsProxy[a] || [];
var b = currentTargetProxy.length;
while (b--) {
// if the same target has a different proxy
if (currentTargetProxy[b].proxy !== proxy) {
// !!IMPORTANT!! store the proxy as a duplicate proxy (dupProxy) -- this will adjust the behavior above appropriately (that is,
// prevent a change on dupProxy from re-triggering the same change on other proxies)
dupProxy = currentTargetProxy[b].proxy;
// make the same delete on the different proxy for the same target object. it is important that we make this change *after* we invoke the same change
// on any other proxies so that the previousValue can show up correct for the other proxies
delete currentTargetProxy[b].proxy[property];
}
}
}
_notifyObservers(changes.length);
return true;
},
set: function(target, property, value, receiver) {
// if the value we're assigning is an object, then we want to ensure
// that we're assigning the original object, not the proxy, in order to avoid mixing
// the actual targets and proxies -- creates issues with path logging if we don't do this
if (value && value.__isProxy) value = value.__getTarget;
// was this change an original change or was it a change that was re-triggered below
var originalChange = true;
if (dupProxy === proxy) {
originalChange = false;
dupProxy = null;
}
// improve performance by saving direct references to the property
var targetProp = target[property];
// Only record this change if:
// 1. the new value differs from the old one
// 2. OR if this proxy was not the original proxy to receive the change
// 3. OR the modified target is an array and the modified property is "length" and our helper property __length indicates that the array length has changed
//
// Regarding #3 above: mutations of arrays via .push or .splice actually modify the .length before the set handler is invoked
// so in order to accurately report the correct previousValue for the .length, we have to use a helper property.
if (targetProp !== value || originalChange === false || (property === "length" && target instanceof Array && target.__length !== value)) {
var foundObservable = true;
var typeOfTargetProp = (typeof targetProp);
// determine if we're adding something new or modifying some that already existed
var type = "update";
if (typeOfTargetProp === "undefined") type = "add";
// store the change that just occurred. it is important that we store the change before invoking the other proxies so that the previousValue is correct
changes.push({
"type":type
,"target":target
,"property":property
,"newValue":value
,"previousValue":receiver[property]
,"currentPath":_getPath(target, property)
,"jsonPointer":_getPath(target, property, true)
,"proxy":proxy
});
// mutations of arrays via .push or .splice actually modify the .length before the set handler is invoked
// so in order to accurately report the correct previousValue for the .length, we have to use a helper property.
if (property === "length" && target instanceof Array && target.__length !== value) {
changes[changes.length-1].previousValue = target.__length;
target.__length = value;
}
// !!IMPORTANT!! if this proxy was the first proxy to receive the change, then we need to go check and see
// if there are other proxies for the same project. if there are, then we will modify those proxies as well so the other
// observers can be modified of the change that has occurred.
if (originalChange === true) {
// because the value actually differs than the previous value
// we need to store the new value on the original target object,
// but only as long as changes have not been paused
if (!observable.changesPaused) target[property] = value;
foundObservable = false;
var targetPosition = target.__targetPosition;
var z = targetsProxy[targetPosition].length;
// find the parent target for this observable -- if the target for that observable has not been removed
// from the targets array, then that means the observable is still active and we should notify the observers of this change
while (z--) {
if (observable === targetsProxy[targetPosition][z].observable) {
if (targets[targetsProxy[targetPosition][z].observable.parentTarget.__targetPosition] !== null) {
foundObservable = true;
break;
}
}
}
// if we didn't find an observable for this proxy, then that means .remove(proxy) was likely invoked
// so we no longer need to notify any observer function about the changes, but we still need to update the
// value of the underlying original objects see below: target[property] = value;
if (foundObservable) {
// loop over each proxy and see if the target for this change has any other proxies
var currentTargetProxy = targetsProxy[targetPosition];
for (var b = 0, l = currentTargetProxy.length; b < l; b++) {
// if the same target has a different proxy
if (currentTargetProxy[b].proxy !== proxy) {
// !!IMPORTANT!! store the proxy as a duplicate proxy (dupProxy) -- this will adjust the behavior above appropriately (that is,
// prevent a change on dupProxy from re-triggering the same change on other proxies)
dupProxy = currentTargetProxy[b].proxy;
// invoke the same change on the different proxy for the same target object. it is important that we make this change *after* we invoke the same change
// on any other proxies so that the previousValue can show up correct for the other proxies
currentTargetProxy[b].proxy[property] = value;
}
}
// if the property being overwritten is an object, then that means this observable
// will need to stop monitoring this object and any nested objects underneath the overwritten object else they'll become
// orphaned and grow memory usage. we execute this on a setTimeout so that the clean-up process does not block
// the UI rendering -- there's no need to execute the clean up immediately
setTimeout(function() {
if (typeOfTargetProp === "object" && targetProp !== null) {
// check if the to-be-overwritten target property still exists on the target object
// if it does still exist on the object, then we don't want to stop observing it. this resolves
// an issue where array .sort() triggers objects to be overwritten, but instead of being overwritten
// and discarded, they are shuffled to a new position in the array
var keys = Object.keys(target);
for (var i = 0, l = keys.length; i < l; i++) {
if (target[keys[i]] === targetProp) return;
}
var stillExists = false;
// now we perform the more expensive search recursively through the target object.
// if we find the targetProp (that was just overwritten) still exists somewhere else
// further down in the object, then we still need to observe the targetProp on this observable.
(function iterate(target) {
var keys = Object.keys(target);
for (var i = 0, l = keys.length; i < l; i++) {
var property = keys[i];
var nestedTarget = target[property];
if (nestedTarget instanceof Object && nestedTarget !== null) iterate(nestedTarget);
if (nestedTarget === targetProp) {
stillExists = true;
return;
}
};
})(target);
// even though targetProp was overwritten, if it still exists somewhere else on the object,
// then we don't want to remove the observable for that object (targetProp)
if (stillExists === true) return;
// loop over each property and recursively invoke the `iterate` function for any
// objects nested on targetProp
(function iterate(obj) {
var keys = Object.keys(obj);
for (var i = 0, l = keys.length; i < l; i++) {
var objProp = obj[keys[i]];
if (objProp instanceof Object && objProp !== null) iterate(objProp);
}
// if there are any existing target objects (objects that we're already observing)...
var c = -1;
for (var i = 0, l = targets.length; i < l; i++) {
if (obj === targets[i]) {
c = i;
break;
}
}
if (c > -1) {
// ...then we want to determine if the observables for that object match our current observable
var currentTargetProxy = targetsProxy[c];
var d = currentTargetProxy.length;
while (d--) {
// if we do have an observable monitoring the object thats about to be overwritten
// then we can remove that observable from the target object
if (observable === currentTargetProxy[d].observable) {
currentTargetProxy.splice(d,1);
break;
}
}
// if there are no more observables assigned to the target object, then we can remove
// the target object altogether. this is necessary to prevent growing memory consumption particularly with large data sets
if (currentTargetProxy.length == 0) {
// targetsProxy.splice(c,1);
targets[c] = null;
}
}
})(targetProp)
}
},10000);
}
// TO DO: the next block of code resolves test case #29, but it results in poor IE11 performance with very large objects.
// UPDATE: need to re-evaluate IE11 performance due to major performance overhaul from 12/23/2018.
//
// if the value we've just set is an object, then we'll need to iterate over it in order to initialize the
// observers/proxies on all nested children of the object
/* if (value instanceof Object && value !== null) {
(function iterate(proxy) {
var target = proxy.__getTarget;
var keys = Object.keys(target);
for (var i = 0, l = keys.length; i < l; i++) {
var property = keys[i];
if (target[property] instanceof Object && target[property] !== null) iterate(proxy[property]);
};
})(proxy[property]);
}; */
};
if (foundObservable) {
// notify the observer functions that the target has been modified
_notifyObservers(changes.length);
}
}
return true;
}
}
var __targetPosition = target.__targetPosition;
if (!(__targetPosition > -1)) {
Object.defineProperty(target, "__targetPosition", {
value: targets.length
,writable: false
,enumerable: false
,configurable: false
});
}
// create the proxy that we'll use to observe any changes
var proxy = new Proxy(target, handler);
// we don't want to create a new observable if this function was invoked recursively
if (observable === null) {
observable = {"parentTarget":target, "domDelay":domDelay, "parentProxy":proxy, "observers":[],"paused":false,"path":path,"changesPaused":false};
observables.push(observable);
}
// store the proxy we've created so it isn't re-created unnecessarily via get handler
var proxyItem = {"target":target,"proxy":proxy,"observable":observable};
// if we have already created a Proxy for this target object then we add it to the corresponding array
// on targetsProxy (targets and targetsProxy work together as a Hash table indexed by the actual target object).
if (__targetPosition > -1) {
// the targets array is set to null for the position of this particular object, then we know that
// the observable was removed some point in time for this object -- so we need to set the reference again
if (targets[__targetPosition] === null) {
targets[__targetPosition] = target;
}
targetsProxy[__targetPosition].push(proxyItem);
// else this is a target object that we had not yet created a Proxy for, so we must add it to targets,
// and push a new array on to targetsProxy containing the new Proxy
} else {
targets.push(target);
targetsProxy.push([proxyItem]);
}
return proxy;
};
/**
* @typedef {object} ObservableSlimChange Observed change.
* @property {"add"|"update"|"delete"} type Change type.
* @property {string} property Property name.
* @property {string} currentPath Property path with the dot notation (e.g. `foo.0.bar`).
* @property {string} jsonPointer Property path with the JSON pointer syntax (e.g. `/foo/0/bar`). See https://datatracker.ietf.org/doc/html/rfc6901.
* @property {object} target Target object.
* @property {ProxyConstructor} proxy Proxy of the target object.
* @property {*} newValue New value of the property.
* @property {*} [previousValue] Previous value of the property
*/
return {
/**
* Create a new ES6 `Proxy` whose changes we can observe through the `observe()` method.
* @param {object} target Plain object that we want to observe for changes.
* @param {boolean|number} domDelay If `true`, then the observed changes to `target` will be batched up on a 10ms delay (via `setTimeout()`).
* If `false`, then the `observer` function will be immediately invoked after each individual change made to `target`. It is helpful to set
* `domDelay` to `true` when your `observer` function makes DOM manipulations (fewer DOM redraws means better performance). If a number greater
* than zero, then it defines the DOM delay in milliseconds.
* @param {function(ObservableSlimChange[])} [observer] Function that will be invoked when a change is made to the proxy of `target`.
* When invoked, this function is passed a single argument: an array of `ObservableSlimChange` detailing each change that has been made.
* @returns {ProxyConstructor} Proxy of the target object.
*/
create: function(target, domDelay, observer) {
// test if the target is a Proxy, if it is then we need to retrieve the original object behind the Proxy.
// we do not allow creating proxies of proxies because -- given the recursive design of ObservableSlim -- it would lead to sharp increases in memory usage
if (target.__isProxy === true) {
var target = target.__getTarget;
//if it is, then we should throw an error. we do not allow creating proxies of proxies
// because -- given the recursive design of ObservableSlim -- it would lead to sharp increases in memory usage
//throw new Error("ObservableSlim.create() cannot create a Proxy for a target object that is also a Proxy.");
}
// fire off the _create() method -- it will create a new observable and proxy and return the proxy
var proxy = _create(target, domDelay);
// assign the observer function
if (typeof observer === "function") this.observe(proxy, observer);
// recursively loop over all nested objects on the proxy we've just created
// this will allow the top observable to observe any changes that occur on a nested object
(function iterate(proxy) {
var target = proxy.__getTarget;
var keys = Object.keys(target);
for (var i = 0, l = keys.length; i < l; i++) {
var property = keys[i];
if (target[property] instanceof Object && target[property] !== null) iterate(proxy[property]);
}
})(proxy);
return proxy;
},
/**
* Add a new observer function to an existing proxy.
* @param {ProxyConstructor} proxy An ES6 `Proxy` created by the `create()` method.
* @param {function(ObservableSlimChange[])} observer Function that will be invoked when a change is made to the proxy of `target`.
* When invoked, this function is passed a single argument: an array of `ObservableSlimChange` detailing each change that has been made.
* @returns {void} Does not return any value.
*/
observe: function(proxy, observer) {
// loop over all the observables created by the _create() function
var i = observables.length;
while (i--) {
if (observables[i].parentProxy === proxy) {
observables[i].observers.push(observer);
break;
}
};
},
/**
* Prevent any observer functions from being invoked when a change occurs to a proxy.
* @param {ProxyConstructor} proxy An ES6 `Proxy` created by the `create()` method.
* @returns {void} Does not return any value.
*/
pause: function(proxy) {
var i = observables.length;
var foundMatch = false;
while (i--) {
if (observables[i].parentProxy === proxy) {
observables[i].paused = true;
foundMatch = true;
break;
}
};
if (foundMatch == false) throw new Error("ObseravableSlim could not pause observable -- matching proxy not found.");
},
/**
* Resume execution of any observer functions when a change is made to a proxy.
* @param {ProxyConstructor} proxy An ES6 `Proxy` created by the `create()` method.
* @returns {void} Does not return any value.
*/
resume: function(proxy) {
var i = observables.length;
var foundMatch = false;
while (i--) {
if (observables[i].parentProxy === proxy) {
observables[i].paused = false;
foundMatch = true;
break;
}
};
if (foundMatch == false) throw new Error("ObseravableSlim could not resume observable -- matching proxy not found.");
},
/**
* Prevent any changes (i.e., `set`, and `deleteProperty`) from being written to the target object.
* However, the observer functions will still be invoked to let you know what changes **WOULD** have been made.
* This can be useful if the changes need to be approved by an external source before the changes take effect.
* @param {ProxyConstructor} proxy An ES6 `Proxy` created by the `create()` method.
* @returns {void} Does not return any value.
*/
pauseChanges: function(proxy){
var i = observables.length;
var foundMatch = false;
while (i--) {
if (observables[i].parentProxy === proxy) {
observables[i].changesPaused = true;
foundMatch = true;
break;
}
};
if (foundMatch == false) throw new Error("ObseravableSlim could not pause changes on observable -- matching proxy not found.");
},
/**
* Resume the changes that were taking place prior to the call to `pauseChanges()` method.
* @param {ProxyConstructor} proxy An ES6 `Proxy` created by the `create()` method.
* @returns {void} Does not return any value.
*/
resumeChanges: function(proxy){
var i = observables.length;
var foundMatch = false;
while (i--) {
if (observables[i].parentProxy === proxy) {
observables[i].changesPaused = false;
foundMatch = true;
break;
}
};
if (foundMatch == false) throw new Error("ObseravableSlim could not resume changes on observable -- matching proxy not found.");
},
/**
* Remove the observable and proxy thereby preventing any further callback observers for changes occurring to the target object.
* @param {ProxyConstructor} proxy An ES6 `Proxy` created by the `create()` method.
* @returns {void} Does not return any value.
*/
remove: function(proxy) {
var matchedObservable = null;
var foundMatch = false;
var c = observables.length;
while (c--) {
if (observables[c].parentProxy === proxy) {
matchedObservable = observables[c];
foundMatch = true;
break;
}
};
var a = targetsProxy.length;
while (a--) {
var b = targetsProxy[a].length;
while (b--) {
if (targetsProxy[a][b].observable === matchedObservable) {
targetsProxy[a].splice(b,1);
// if there are no more proxies for this target object
// then we null out the position for this object on the targets array
// since we are essentially no longer observing this object.
// we do not splice it off the targets array, because if we re-observe the same
// object at a later time, the property __targetPosition cannot be redefined.
if (targetsProxy[a].length === 0) {
targets[a] = null;
};
}
};
};
if (foundMatch === true) {
observables.splice(c,1);
}
}
};
})();
// Export in a try catch to prevent this from erroring out on older browsers
try { module.exports = ObservableSlim; } catch (err) {};