I m not able to override the function 'onmousedown' from the class
Ext.util.Floating.
the sample is given below.
Is there some pattern to follow if i want to override functions with 'on' prefix?
constructor is getting invoked form the overridden code block but 'onMouseDown' still reverts back to the ext-all-debug file.
Ext.define('Ext.util.Floating.override', {
override: 'Ext.util.Floating',
constructor: function(){console.log('onmousedown: This gets invoked.')},
onMouseDown: function (e) {
console.log('OverrideOnMouseDown');
var focusTask = this.focusTask;
if (this.floating && (!focusTask || !focusTask.id)) {
this.toFront(!!e.getTarget(':focusable'));
}
}
});
The constructor of the class 'Ext.util.Floating' was hardcoded to pick up the method 'onMouseDown' with out checking for any override.
I overrode the constructor as well and implemented the check of override on 'onMouseDown' existence.
Ext.define('Ext.util.Floating.override', {
override: 'Ext.util.Floating',
constructor: function(){
.
.
.
me.mon(me.el, {
//redirects to the overridden method we provided.
mousedown: me.mixins.floating.onMouseDown ? me.mixins.floating.onMouseDown: me.onMouseDown,
scope: me
});
.
.
.
},
onMouseDown: function (e) {
console.log('OverrideOnMouseDown');
var focusTask = this.focusTask;
if (this.floating && (!focusTask || !focusTask.id)) {
this.toFront(!!e.getTarget(':focusable'));
}
}
});
Related
What is the difference between class method, class property which is a function, and class property which is an arrow function? Does the this keyword behave differently in the different variants of the method?
class Greeter {
constructor() {
this.greet();
this.greet2();
this.greet3();
}
greet() {
console.log('greet1', this);
}
greet2 = () => {
console.log('greet2', this);
}
greet3 = function() {
console.log('greet3', this);
}
}
let bla = new Greeter();
This is the resulting JavaScript when transpiled from TypeScript.
var Greeter = /** #class */ (function () {
function Greeter() {
var _this = this;
this.greet2 = function () {
console.log('greet2', _this);
};
this.greet3 = function () {
console.log('greet3', this);
};
this.greet();
this.greet2();
this.greet3();
}
Greeter.prototype.greet = function () {
console.log('greet1', this);
};
return Greeter;
}());
var bla = new Greeter();
My TypeScript version is 3.4.5.
There are differences between all 3 versions. This differences are in 3 areas:
Who is this at runtime
Where the function is assigned
What is the type of this in typescript.
Lets start with where they work just the same. Consider this class, with a class field:
class Greeter {
constructor(private x: string) {
}
greet() {
console.log('greet1', this.x);
}
greet2 = () => {
console.log('greet2', this.x);
}
greet3 = function () {
// this is typed as any
console.log('greet3', this.x);
}
}
let bla = new Greeter(" me");
With this class all 3 function calls will print as expected: 'greet* me' when invoked on bla
bla.greet()
bla.greet2()
bla.greet3()
Who is this at runtime
Arrow functions capture this from the declaration context, so this in greet2 is always guaranteed to be the class instance that created this function. The other versions (the method and function) make no such guarantees.
So in this code not all 3 print the same text:
function call(fn: () => void) {
fn();
}
call(bla.greet) // greet1 undefined
call(bla.greet2) //greet2 me
call(bla.greet3) // greet3 undefined
This is particularly important when passing the function as an event handler to another component.
Where the function is assigned
Class methods (such as greet) are assigned on the prototype, field initializations (such as greet2 and greet3) are assigned in the constructor. This means that greet2 and greet3 will have a larger memory footprint as they require an allocation of a fresh closure each time Greeter is instantiated.
What is the type of this in typescript.
Typescript will type this as an instance of Greeter in both the method (greet) and the arrow function (greet2) but will type this as any in greet3. This will make it an error if you try to use this in greet3 under noImplictAny
When to use them
Use the method syntax if this function will not be passed as an event handler to another component (unless you use bind or something else to ensure this remains the instance of the class)
Use arrow function syntax when your function will be passed around to other components and you need access to this inside the function.
Can't really think of a good use case for this, generally avoid.
this keyword difference:
In the above all three have same this but you will see the difference when you will pass the method to another functions.
class Greeter {
constructor() {
}
greet() {
console.log(this);
}
greet2 = () => {
console.log(this);
}
greet3 = function() {
console.log(this);
}
}
let bla = new Greeter();
function wrapper(f){
f();
}
wrapper(bla.greet) //undefined
wrapper(bla.greet2) //Greeter
wrapper(bla.greet3) //undefined
But there is another difference that the first method is on the prototype of class while other two are not. They are the method of instance of object.
class Greeter {
constructor() {
}
greet() {
console.log('greet1', this);
}
greet2 = () => {
console.log('greet2', this);
}
greet3 = function() {
console.log('greet3', this);
}
}
let bla = new Greeter();
console.log(Object.getOwnPropertyNames(Greeter.prototype))
If I have in the class -> str = "my string"; and in all the 3 methods I can say console.log(this.str) and it outputs the "my string". But I wonder - is this really actually the same thing
No they are not same things. As I mentioned that greet2 and greet3 will not be on Greeter.prototype instead they will be on the instance itself. It mean that if you create 1000 instances of Greeter their will be 1000 different method(greet2 and greet3) stored in memory for 1000 different instances. But there will a single greet method for all the instances.
See the below snippet with two instances of Greeter()
I'm using a TypeScript class to define a controller in AngularJS:
class TrialsCtrl {
constructor(private $scope: ITrialsScope, private ResourceServices: ResourceServices) {
this.loadTrials();
}
loadTrials() {
console.log("TrialsCtrl:", this);
this.Trial.query().then((result) => {
this.$scope.Trials = result;
});
}
remove(Trial: IRestTrial) {
this.ResourceServices.remove(Trial, this.loadTrials);
}
}
angular.module("app").controller("TrialsCtrl", TrialsCtrl);
I'm refactoring common controller methods into a service.
class ResourceServices {
public remove(resource, reload) {
if (confirm("Are you sure you want to delete this?")) {
resource.remove().then(() => {
reload();
});
}
}
}
angular.module("app").service("ResourceServices", ResourceServices);
The console log shows that this is referencing the window context when I want it to be TrialsCtrl. My problem is that the reload() method needs to run in the context of TrialsCtrl, so that it can access this.Trial and this.$scope. How can I tell the reload() method to set this as the TrialsCtrl? Or is there some other workaround I should be using for this kind of thing?
Have you tried:
this.ResourceServices.remove(Trial, this.loadTrials.bind(this));
or
this.ResourceServices.remove(Trial, () => this.loadTrials());
For methods that are supposed to be passed as callbacks (as with this.loadTrials) it is preferable to define them as arrows,
loadTrials = () => { ... }
So they keep the context whether Function.prototype.bind is used or not.
Alternatively, a decorator may be used on the method (like core-decorators #autobind) to bind a method while still defining it on class prototype:
#autobind
loadTrials() { ... }
I try to use jstree control in my TypeScript code for an angularjs application. I use jstree typings and jstree.directive to show a tree. Everything works to the point when I need to handle menu item click and call for the base method. Inside of my action there is no "this" (contextmenu) scope. Any suggestions?
class MapTreeViewController {
mapTreeView: JSTree;
vm.mapTreeView = $('#jstree').jstree(
{
'core': { 'data': items },
'plugins': ['themes', 'ui', 'contextmenu'],
'contextmenu': {
'items': function(node:any) {
var vmNode = this;
return {
'rename': { // rename menu item
'label': 'Rename',
'action': function(obj) {
this.rename(obj);
}
}
};
}
}
});
}
Somewhere inside of a method.
this is not an instance - take a look at the original function to see how to obtain an instance:
https://github.com/vakata/jstree/blob/master/src/jstree.contextmenu.js#L84
"action" : function (data) {
var inst = $.jstree.reference(data.reference),
...
I started using typescript together with angularjs. I have written a simple class that is responsible for drag and drop behavior (or will be in future). But right now in my handleDragEnd function when I access canvas element I get error
Cannot read property of undefined
Below is my code - if someone could tell me what I am doing wrong I would be grateful.
class ToolBox {
private canvas;
constructor(canvas)
{
this.canvas = canvas;
$(".beacon").draggable({
helper: 'clone',
cursor: 'pointer',
start: this.handleDragStart,
stop: this.handleDragEnd
});
}
handleDragStart()
{
console.log('Drag Started!');
}
handleDragEnd()
{
var pointer = this.canvas.getPointer(event.e);
console.log('Drag End!');
return;
}
}
Since class methods are defined on ToolBox.prototype, the value of this is getting lost when you pass in the methods directly.
Change:
start: this.handleDragStart,
stop: this.handleDragEnd
To:
start: () => this.handleDragStart(),
stop: () => this.handleDragEnd()
That will preserve the value of this by calling the methods on the instance.
I want to define a class with utility functions. I'm using Extjs class system.
I'm doing this in the following way:
Ext.ns('Controls.Plugins.Nzok')
Ext.define('Controls.Plugins.Nzok.XUtility', {
statics : {
getTest : function(test) { return test }
}
})
Now when I want to use getTest method I have to require the class and to write full class name
Ext.define('Controls.Plugins.Nzok', {
requires : ['Controls.Plugins.Nzok.XUtility'],
useTest : function() {
var testResult = Controls.Plugins.Nzok.XUtility.getTest(2);
}
})
My problem is that notation is too long. It's very inconvenient to write down every time Controls.Plugins.Nzok.XUtility. Are there any solution?
The alternateClassName config does the trick.
Ext.define('Controls.Plugins.Nzok.XUtility', {
alternateClassName: 'Controls.XUtil', // <--- this is your shorthand
statics : {
getTest : function(test) { return test }
}
});
As a side note, Ext.define will automatically create namespaces based on your class name, so Ext.define('Controls.Plugins.Nzok.XUtility' will generate the Controls.Plugins.Nzok namespace for you.