I would like to create a canvas in which I would load images of some entity. the images of these entities could change from time to time.
FabricJs provides a built in serialization & de-serialization mechanism using following methods
fabric.Canvas#toJSON to serialize the canvas and
fabric.Canvas#loadFromJSON to de-serialize it but the problem with them is they serialize the image source as well which is enormous and useless in my case
(fabric.Canvas#toDatalessJSON & fabric.Canvas#loadFromDatalessJSON seems to work only for complex object but not images gitHub Ref)
whats is the approach to this?
should customize serialization by serializing all the required properties and recreate objects based on those info?
I have even try to create a subclass of Image removing src from toObject to avoid serializing it but it seems that does not work as well
here is what I have tried with subclass
fabric.MyImage = fabric.util.createClass(fabric.Image, {
type: 'MyImage',
initialize: function(options) {
options || (options = { })
this.callSuper('initialize', options)
this.set('artIndexes', options.artIndexes || '')
},
toObject: function() {
const TO = this.callSuper('toObject')
fabric.util.object.extend(TO, {
artIndexes: this.get('artIndexes')
})
delete TO.src
return TO
},
_render: function(ctx) {
this.callSuper('_render', ctx)
}// ,
// fromURL: function(a, b) {
// this.callSuper('fromURL', a, b)
// }
})
fabric.MyImage.fromObject = function (object, callback) {
fabric.util.enlivenObjects(object.objects, function (enlivenedObjects) {
delete object.objects
callback && callback(new fabric.MyImage(enlivenedObjects, object))
})
}
fabric.MyImage.async = true
and to add Image i would do somthing like this
let img = new fabric.MyImage({entetyReference: entetyRef})
img.setSrc(`${imageSource}`, image => {
this.canvas.add(img)
})
but during serialization and de-serializatiin using FabricJs provided method the object get lost from canvas
I am using latest version of fabricJs
Using knockout.js in node, how can I get a reference to a child VM component, which was invoked from a template?
Illustration
I have a Question Model, VM, containining a custom Resource component, with it's respective Model and VM. The Resource VM registers a custom component and receives a Resource Model object as a parameter, which was constructed by the parent Question Model. This constructed resource is passed as a parameter with the template:
QuestionModel.js
this = new QuestionModel(...);
this.resource = new ResourceModel(some data);
question-template.html
<div data-bind="foreach: { data: questions, as: 'question' }">
<!-- question related -->
<resource params="resource: question.resource"></resource>
</div>
ResourceVM.js
define(function(require, exports, module) {
var ko = require('knockout');
var ResourceViewModel = function ResourceViewModel(params) {
this.resource = params.resource;
this.somethingSpecific = function() {
return 'some value manipulate from this model';
}
}
ko.components.register('resource', {
viewModel: {
createViewModel: function(params, componentInfo) {
return new ResourceViewModel(params);
}
},
template: {
require: 'text!/resource-template.html'
}
});
return ResourceViewModel;
});
I want to be able to call functions of the Resource VM (like question.resourceVM.somethingSpecific()).
What is a proper way of getting a reference to a component child?
The only solution I can think of is to pass the parent object with the parameters and extend it from child, which is obviously bad.
Your QuestionModel already has access to this.resource, so the way forward might be by doing it through the data models, instead of through the view models. Having somethingSpecific() as an attribute on either QuestionModel or ResourceModel instead of ResourceViewModel would solve the problem nicely.
I would argue that manipulating data is the responsibility of the entity that holds it; the job of the ResourceViewModel is only to provide glue between the data model and the DOM.
var QuestionModel = function QuestionModel() {
this.somethingSpecific = function somethingSpecific() {
this.resource.doStuff();
};
};
this = new QuestionModel();
this.resource = new ResourceModel(some data);
You could then give your resource component access to the question instead of the child resource:
var ResourceViewModel = function ResourceViewModel(params) {
this.question = params.question;
this.resource = this.question.resource;
}
Having trouble debugging an issue that mockgoose has for populating a property with fields set. Yads mockgoose http://github.com/yads/Mockgoose fork solved the bug of making the populate option work, but if you specify fields it returns a null for the populated property. I tried looking through the source code and stepping through with the debugger but not sure where to look. I can see in the debugger that the populate option triggers a call to get the child element - and I see the call made returns the right child result with the correct fields, but when the parent element finally comes back it has the property to the child element set to null.
The query:
Posts.findById(foo).populate('createdBy', {fname:1, lname:1});
Incorrectly returns a post with post.createdBy = null. Omitting the fields parameter of fame, lname, somehow makes it work again with post.createdBy returning the full object.
Following are some excerpts from the code - though I'm not sure those are the right places to look.
collections.js
this.find = function (conditions, options, callback) {
var results;
var models = db[name];
if (!_.isEmpty(conditions)) {
results = utils.findModelQuery(models, conditions);
} else {
results = utils.objectToArray(utils.cloneItems(models));
}
results = filter.applyOptions(options, results);
if (results.name === 'MongoError') {
callback(results);
} else {
var result = {
toArray: function (callback) {
callback(null, results);
}
};
callback(null, result);
}
};
util.js
function cloneItems(items) {
var clones = {};
for (var item in items) {
clones[item] = cloneItem(items[item]);
}
return clones;
}
function cloneItem(item) {
return _.cloneDeep(item, function(value) {
// Do not clone items that are ObjectId objects as _.clone mangles them
if (value instanceof ObjectId) {
return new ObjectId(value.toString());
}
});
}
And here's a conversation about the issue
https://github.com/mccormicka/Mockgoose/pull/90
I need to introduce few additional properties to existing object properties set.
like:
ID
Geo Location
etc
Whenever I draw a shape, I need to add additional properties to the shape and need to get from toDataLessJSON()
As of version 1.7.0 levon's code stopped working. All you need to do is to fix as follows:
// Save additional attributes in Serialization
fabric.Object.prototype.toObject = (function (toObject) {
return function (properties) {
return fabric.util.object.extend(toObject.call(this, properties), {
textID: this.textID
});
};
})(fabric.Object.prototype.toObject);
You have to receive properties argument and pass it on to toObject.
Here's a code for adding custom properties and saving them in JSON serialization for any object on canvas. (I used standard javascript object properties, but it works for me)
canvas.myImages = {};
fabric.Image.fromURL('SOME-IMAGE-URL.jpg', function(img) {
canvas.myImages.push(img);
var i = canvas.myImages.length-1;
canvas.myImages[i].ID = 1; // add your custom attributes
canvas.myImages[i].GeoLocation = [40, 40];
canvas.add(canvas.myImages[i]);
canvas.renderAll();
});
And you then include the custom attribute in object serialization.
// Save additional attributes in Serialization
fabric.Object.prototype.toObject = (function (toObject) {
return function () {
return fabric.util.object.extend(toObject.call(this), {
textID: this.textID
});
};
})(fabric.Object.prototype.toObject);
// Test Serialization
var json = JSON.stringify(canvas.toDatalessJSON());
console.log(json);
canvas.clear();
// and load everything from the same json
canvas.loadFromDatalessJSON(json, function() {
// making sure to render canvas at the end
canvas.renderAll();
}
I am aware of how to create getters and setters for properties whose names one already knows, by doing something like this:
// A trivial example:
function MyObject(val){
this.count = 0;
this.value = val;
}
MyObject.prototype = {
get value(){
return this.count < 2 ? "Go away" : this._value;
},
set value(val){
this._value = val + (++this.count);
}
};
var a = new MyObject('foo');
alert(a.value); // --> "Go away"
a.value = 'bar';
alert(a.value); // --> "bar2"
Now, my question is, is it possible to define sort of catch-all getters and setters like these? I.e., create getters and setters for any property name which isn't already defined.
The concept is possible in PHP using the __get() and __set() magic methods (see the PHP documentation for information on these), so I'm really asking is there a JavaScript equivalent to these?
Needless to say, I'd ideally like a solution that is cross-browser compatible.
This changed as of the ES2015 (aka "ES6") specification: JavaScript now has proxies. Proxies let you create objects that are true proxies for (facades on) other objects. Here's a simple example that turns any property values that are strings to all caps on retrieval, and returns "missing" instead of undefined for a property that doesn't exist:
"use strict";
if (typeof Proxy == "undefined") {
throw new Error("This browser doesn't support Proxy");
}
let original = {
example: "value",
};
let proxy = new Proxy(original, {
get(target, name, receiver) {
if (Reflect.has(target, name)) {
let rv = Reflect.get(target, name, receiver);
if (typeof rv === "string") {
rv = rv.toUpperCase();
}
return rv;
}
return "missing";
}
});
console.log(`original.example = ${original.example}`); // "original.example = value"
console.log(`proxy.example = ${proxy.example}`); // "proxy.example = VALUE"
console.log(`proxy.unknown = ${proxy.unknown}`); // "proxy.unknown = missing"
original.example = "updated";
console.log(`original.example = ${original.example}`); // "original.example = updated"
console.log(`proxy.example = ${proxy.example}`); // "proxy.example = UPDATED"
Operations you don't override have their default behavior. In the above, all we override is get, but there's a whole list of operations you can hook into.
In the get handler function's arguments list:
target is the object being proxied (original, in our case).
name is (of course) the name of the property being retrieved, which is usually a string but could also be a Symbol.
receiver is the object that should be used as this in the getter function if the property is an accessor rather than a data property. In the normal case this is the proxy or something that inherits from it, but it can be anything since the trap may be triggered by Reflect.get.
This lets you create an object with the catch-all getter and setter feature you want:
"use strict";
if (typeof Proxy == "undefined") {
throw new Error("This browser doesn't support Proxy");
}
let obj = new Proxy({}, {
get(target, name, receiver) {
if (!Reflect.has(target, name)) {
console.log("Getting non-existent property '" + name + "'");
return undefined;
}
return Reflect.get(target, name, receiver);
},
set(target, name, value, receiver) {
if (!Reflect.has(target, name)) {
console.log(`Setting non-existent property '${name}', initial value: ${value}`);
}
return Reflect.set(target, name, value, receiver);
}
});
console.log(`[before] obj.example = ${obj.example}`);
obj.example = "value";
console.log(`[after] obj.example = ${obj.example}`);
The output of the above is:
Getting non-existent property 'example'
[before] obj.example = undefined
Setting non-existent property 'example', initial value: value
[after] obj.example = value
Note how we get the "non-existent" message when we try to retrieve example when it doesn't yet exist, and again when we create it, but not after that.
Answer from 2011 (obsoleted by the above, still relevant to environments limited to ES5 features like Internet Explorer):
No, JavaScript doesn't have a catch-all property feature. The accessor syntax you're using is covered in Section 11.1.5 of the spec, and doesn't offer any wildcard or something like that.
You could, of course, implement a function to do it, but I'm guessing you probably don't want to use f = obj.prop("example"); rather than f = obj.example; and obj.prop("example", value); rather than obj.example = value; (which would be necessary for the function to handle unknown properties).
FWIW, the getter function (I didn't bother with setter logic) would look something like this:
MyObject.prototype.prop = function(propName) {
if (propName in this) {
// This object or its prototype already has this property,
// return the existing value.
return this[propName];
}
// ...Catch-all, deal with undefined property here...
};
But again, I can't imagine you'd really want to do that, because of how it changes how you use the object.
Preface:
T.J. Crowder's answer mentions a Proxy, which will be needed for a catch-all getter/setter for properties which don't exist, as the OP was asking for. Depending on what behavior is actually wanted with dynamic getters/setters, a Proxy may not actually be necessary though; or, potentially, you may want to use a combination of a Proxy with what I'll show you below.
(P.S. I have experimented with Proxy thoroughly in Firefox on Linux recently and have found it to be very capable, but also somewhat confusing/difficult to work with and get right. More importantly, I have also found it to be quite slow (at least in relation to how optimized JavaScript tends to be nowadays) - I'm talking in the realm of deca-multiples slower.)
To implement dynamically created getters and setters specifically, you can use Object.defineProperty() or Object.defineProperties(). This is also quite fast.
The gist is that you can define a getter and/or setter on an object like so:
let obj = {};
let val = 0;
Object.defineProperty(obj, 'prop', { //<- This object is called a "property descriptor".
//Alternatively, use: `get() {}`
get: function() {
return val;
},
//Alternatively, use: `set(newValue) {}`
set: function(newValue) {
val = newValue;
}
});
//Calls the getter function.
console.log(obj.prop);
let copy = obj.prop;
//Etc.
//Calls the setter function.
obj.prop = 10;
++obj.prop;
//Etc.
Several things to note here:
You cannot use the value property in the property descriptor (not shown above) simultaneously with get and/or set; from the docs:
Property descriptors present in objects come in two main flavors: data descriptors and accessor descriptors. A data descriptor is a property that has a value, which may or may not be writable. An accessor descriptor is a property described by a getter-setter pair of functions. A descriptor must be one of these two flavors; it cannot be both.
Thus, you'll note that I created a val property outside of the Object.defineProperty() call/property descriptor. This is standard behavior.
As per the error here, don't set writable to true in the property descriptor if you use get or set.
You might want to consider setting configurable and enumerable, however, depending on what you're after; from the docs:
configurable
true if and only if the type of this property descriptor may be changed and if the property may be deleted from the corresponding object.
Defaults to false.
enumerable
true if and only if this property shows up during enumeration of the properties on the corresponding object.
Defaults to false.
On this note, these may also be of interest:
Object.getOwnPropertyNames(obj): gets all properties of an object, even non-enumerable ones (AFAIK this is the only way to do so!).
Object.getOwnPropertyDescriptor(obj, prop): gets the property descriptor of an object, the object that was passed to Object.defineProperty() above.
obj.propertyIsEnumerable(prop);: for an individual property on a specific object instance, call this function on the object instance to determine whether the specific property is enumerable or not.
The following could be an original approach to this problem:
var obj = {
emptyValue: null,
get: function(prop){
if(typeof this[prop] == "undefined")
return this.emptyValue;
else
return this[prop];
},
set: function(prop,value){
this[prop] = value;
}
}
In order to use it the properties should be passed as strings.
So here is an example of how it works:
//To set a property
obj.set('myProperty','myValue');
//To get a property
var myVar = obj.get('myProperty');
Edit:
An improved, more object-oriented approach based on what I proposed is the following:
function MyObject() {
var emptyValue = null;
var obj = {};
this.get = function(prop){
return (typeof obj[prop] == "undefined") ? emptyValue : obj[prop];
};
this.set = function(prop,value){
obj[prop] = value;
};
}
var newObj = new MyObject();
newObj.set('myProperty','MyValue');
alert(newObj.get('myProperty'));
You can see it working here.
I was looking for something and I figured out on my own.
/*
This function takes an object and converts to a proxy object.
It also takes care of proxying nested objectsa and array.
*/
let getProxy = (original) => {
return new Proxy(original, {
get(target, name, receiver) {
let rv = Reflect.get(target, name, receiver);
return rv;
},
set(target, name, value, receiver) {
// Proxies new objects
if(typeof value === "object"){
value = getProxy(value);
}
return Reflect.set(target, name, value, receiver);
}
})
}
let first = {};
let proxy = getProxy(first);
/*
Here are the tests
*/
proxy.name={} // object
proxy.name.first={} // nested object
proxy.name.first.names=[] // nested array
proxy.name.first.names[0]={first:"vetri"} // nested array with an object
/*
Here are the serialised values
*/
console.log(JSON.stringify(first)) // {"name":{"first":{"names":[{"first":"vetri"}]}}}
console.log(JSON.stringify(proxy)) // {"name":{"first":{"names":[{"first":"vetri"}]}}}
var x={}
var propName = 'value'
var get = Function("return this['" + propName + "']")
var set = Function("newValue", "this['" + propName + "'] = newValue")
var handler = { 'get': get, 'set': set, enumerable: true, configurable: true }
Object.defineProperty(x, propName, handler)
this works for me