I am authoring a plugin which instantiates a map. The map would then provide a function to move to another place on the earth.
The script makes the map just fine. However I can't "tack" the function on the element, to be used by another plugin in a callback.
Here's the approach I tried; in plugin:
(function($){
$.fn.mapDo(options){
map = new BlahMap(this.get(0));
this.moveTheMap = function(place){
map.moveItToThat(place);
}; // nope.
}
})(jQuery);
Then, in view:
$(map).mapDo();
$(otherElement).otherControl({
callback: function(place){
$(map).moveTheMap(place); // moveTheMap is not there on $(map)!
}
};
The Question
How do I add a function to the map jQuery or DOM element, if possible? If not, how can I provide that kind of functionality?
More importantly, am I going the right way here by separating the things that way? I'm a bit of a neophyte to Javascript, how are these tasks usually done while still keeping the components apart?
While that's the stab I took at it, more generally, I struggled with the concept of outputting things from a jQuery plugin while maintaining chainability. In this case, what I am trying to do is to output a callback from the plugin that will work on the called element later in the execution.
Plugins normally only add one method to the jQuery prototype, and the method calls to the plugin's instances are done with strings.
(function($) {
$.fn.mapDo = function(options) {
var args = [].slice.call(arguments, 1); //Get all the arguments starting from 2nd argument as an array
return this.each(function() {
var $this = $(this),
instance = $this.data("map-instance");
if (!instance) {
$this.data("map-instance", (instance = new BlahMap(this, options)));
}
if (typeof options == "string") {
instance[options].apply(instance, args);
}
});
};
})(jQuery);
$(elem).mapDo( "moveTheMap", place ); //This would also instantiate the plugin if it wasn't instantiated
Here's jsfiddle showing it in action:
http://jsfiddle.net/X8YA8/1/
You could store the map with .data method.
(function($){
$.fn.mapDo = funciont(options) {
this.data('map', new BlahMap(this.get(0)));
return this;
};
$.fn.moveTheMap = function(place) {
var map = this.data('map');
if (map) {
map.moveItToThat(place);
}
return this;
};
})(jQuery);
Related
I create a simple jQuery extension(it's my first).
(function($){
var MyClass = function(opt){
//..
};
//one of the methods of my extension
$.fn.myExtension = function(opt){
this._ext = new MyClass(opt);
return this;
};
$.fn.myExtensionOtherMethod = function(){
if(this._ext){
//do something ..
}
return this;
};
}(jQuery));
//using ..
$(document).ready(function(){
$('#selector').myExtension({
//options ..
});
$('#selector').myExtensionOtherMethod();
});
when i invoke method $('#selector').myExtensionOtherMethod();, this does not contains this._ext variable. I know that this is other scope, but i know that there is some way to access that variable in both methods.how can i do it?
This isn't really a scope issue. This is because the jQuery prototype $.fn gives you a jquery object as this. Even though you are selecting the same element each time its a new jQuery object set as the context so that property is gone. You can put that property on the DOM element and achieve the outcome you want.
(function($) {
var MyClass = function(opt) {};
//one of the methods of my extension
$.fn.myExtension = function(opt) {
this[0]._ext = new MyClass(opt);
return this;
};
$.fn.myExtensionOtherMethod = function() {
if (this[0]._ext) {
//do something ..
}
return this;
};
}(jQuery));
//using ..
$(document).ready(function() {
$('#selector').myExtension({
//options ..
});
$('#selector').myExtensionOtherMethod();
});
This is just a quick example above. If your selector finds more than one element you should loop though them. But I only grabbed the first index since you were selecting by ID.
Fiddle: https://jsfiddle.net/AtheistP3ace/gd1ehk0d/
As mentioned above by #charlietfl, I agree with that comment. Happy to explain why what you did didn't work but there may be better ways to achieve what you are looking for.
I'd like to 'proxy' (not sure if that's the term at all) a function inside a function object for easy calling.
Given the following code
function Soldier() {
this.el = $("<div></div>").addClass('soldier');
this.pos = this.el.position; // $(".soldier").position(), or so I thought
}
In the console:
s = new Soldier();
$("#gamemap").append(s.el); // Add the soldier to the game field
s.pos === s.el.position // this returns true
s.el.position() // Returns Object {top: 0, left: 0}
s.pos() // Returns 'undefined'
What am I doing wrong in this scenario and is there an easy way to achieve my goal (s.pos() to return the result of s.el.position()) ?
I thought about s.pos = function() { return s.el.position(); } but looks a bit ugly and not apropriate. Also I'd like to add more similar functions and the library will become quite big to even load.
When you're calling s.pos(), its this context is lost.
You can simulate this behavior using call():
s.pos.call(s); // same as s.pos()
s.pos.call(s.el); // same as s.el.position()
This code is actually ok:
s.pos = function() { return s.el.position(); }
An alternative is using bind():
s.pos = s.el.position.bind(el);
You can use the prototype, that way the functions will not be created separately for every object:
Soldier.prototype.pos = function(){ return this.el.position(); }
I'd recommend to use the prototype:
Soldier.prototype.pos = function() { return this.el.position(); };
Not ugly at all, and quite performant actually.
If you want to directly assign it in the constructor, you'll need to notice that the this context of a s.pos() invocation would be wrong. You therefore would need to bind it:
…
this.pos = this.el.position.bind(this.el);
It's because the context of execution for position method has changed. If you bind the method to work inside the element context it will work.
JS Fiddle
function Soldier() {
this.el = $("<div></div>").addClass('soldier');
this.pos = this.el.position.bind(this.el);
}
var s = new Soldier();
$("#gamemap").append(s.el);
console.log(s.pos());
I've been working on writing a custom jquery plugin for one of my web applications but I've been running into a strange error, I think it's due to my unfamiliarity with object-oriented programming.
The bug that I've been running into comes when I try to run the $(".list-group").updateList('template', 'some template') twice, the first time it works just fine, but the second time I run the same command, I get an object is not a function error. Here's the plugin code:
(function($){
defaultOptions = {
defaultId: 'selective_update_',
listSelector: 'li'
};
function UpdateList(item, options) {
this.options = $.extend(defaultOptions, options);
this.item = $(item);
this.init();
console.log(this.options);
}
UpdateList.prototype = {
init: function() {
console.log('initiation');
},
template: function(template) {
// this line is where the errors come
this.template = template;
},
update: function(newArray) {
//update code is here
// I can run this multiple times in a row without it breaking
}
}
// jQuery plugin interface
$.fn.updateList = function(opt) {
// slice arguments to leave only arguments after function name
var args = Array.prototype.slice.call(arguments, 1);
return this.each(function() {
var item = $(this), instance = item.data('UpdateList');
if(!instance) {
// create plugin instance and save it in data
item.data('UpdateList', new UpdateList(this, opt));
} else {
// if instance already created call method
if(typeof opt === 'string') {
instance[opt](args);
}
}
});
}
}(jQuery));
One thing I did notice when I went to access this.template - It was in an array so I had to call this.template[0] to get the string...I don't know why it's doing that, but I suspect it has to do with the error I'm getting. Maybe it can assign the string the first time, but not the next? Any help would be appreciated!
Thanks :)
this.template = template
Is in fact your problem, as you are overwriting the function that is set on the instance. You end up overwriting it to your args array as you pass that as your argument to the initial template function. It basically will do this:
this.template = ["some template"];
Thus the next time instance[opt](args) runs it will try to execute that array as if it were a function and hence get the not a function error.
JSFiddle
I've a page that is generated dynamically, and that includes certain number (user-dynamically-defined) of advanced scatter plot charts. I intend to create a JavaScript object which defines the scatter plot itself, i.e. which takes some parameters, some data, and some container ID, and which will create the various elements needed to obtain the visualisation: canvas elements, toolbar, etc.. To do so, I started with the following (simplified) class:
(function () {
if (!this.namespace) { this.namespace = {};}
this._instances = { index: 0 };
this.namespace.ScatterPlot = function (containerId, file, options) {
_instances.index ++;
this.id = this.containerId+"-"+_instances.index ;
this.containerId = containerId ;
_instances [this.id] = this;
// ... Do stuffs with file and options ...
// Initialize elements once the DOM is ready
$(this.updateDOM);
}
namespace.ScatterPlot.prototype = {
updateDOM: function() {
$("<canvas>")
.click(clickCallback)
.appendTo("#"+this.containerId);
//(...)
},
clickCallback: function() {
alert("Some click: "+this.id);
}
}
})();
Each object can be created with:
var v1 = new namespace.ScatterPlot("container1", "foo", "foo");
var v2 = new namespace.ScatterPlot("container2", "foo", "foo");
There are two problems here: (1) in updateDOM, 'this' does not make reference to my initial ScatterPlot object, which means that this example will never work, and (2) similarly, the clickCallback will not be able reference the scatterplot with 'this' either.
I'm new to javascript, and I'm still struggeling to understand the logic of OO programming in javascript, so the question is: I'm I taking the wrong direction here ? After some digging, I could roughly achieve what I wanted by passing this to updateDOM:
$(this.updateDOM(this)); // This blows my eyes but does the trick, at least partially
updateDOM: function(that) {
$("<canvas>")
.click(that.clickCallback)
.appendTo("#"+that.containerId);
//(...)
},
clickCallback: function() {
// Not working either... Should pass 'that' to the function too
alert("Some click: "+this.id);
}
But I don't feel this patters to be very elegant... And the problem is not fixed either regarding the click callback.
Thoughts ?
Have a look at MDN's introduction to the this keyword.
The standard ways of dealing with that issue are using a that variable - not as an argument, but in a separate function:
var that = this;
$(function() {
that.updateDOM();
});
// or
$(this.getClickCallback());
...
namespace.ScatterPlot.prototype.getClickCallback = function() {
var that = this;
return function clickCallback(e) {
alert("Some click: "+that.id);
};
};
Alternatively, you can always use .bind() (or $.proxy for older browsers) which do quite what the second example does in a more generic way:
$(this.clickCallback.bind(this));
Hi I'm trying to author a jQuery plugin and I need to have methods accessible to elements after they are initialized as that kind of object, e.g.:
$('.list').list({some options}); //This initializes .list as a list
//now I want it to have certain methods like:
$('.list').find('List item'); //does some logic that I need
I tried with
$.fn.list = function (options) {
return this.each(function() {
// some code here
this.find = function(test) {
//function logic
}
}
}
and several other different attempts, I just can't figure out how to do it.
EDIT:
I'll try to explain this better.
I'm trying to turn a table into a list, basically like a list on a computer with column headers and sortable items and everything inbetween. You initiate the table with a command like
$(this).list({
data: [{id: 1, name:'My First List Item', date:'2010/06/26'}, {id:2, name:'Second', date:'2010/05/20'}]
});
.list will make the <tbody> sortable and do a few other initial tasks, then add the following methods to the element:
.findItem(condition) will allow you to find a certain item by a condition (like findItem('name == "Second"')
.list(condition) will list all items that match a given condition
.sort(key) will sort all items by a given key
etc.
What's the best way to go about doing this?
If you want these methods to be available on any jQuery object, you will have to add each one of them to jQuery's prototype. The reason is every time you call $(".list") a fresh new object is created, and any methods you attached to a previous such object will get lost.
Assign each method to jQuery's prototype as:
jQuery.fn.extend({
list: function() { .. },
findItem: function() { .. },
sort: function() { .. }
});
The list method here is special as it can be invoked on two occasions. First, when initializing the list, and second when finding particular items by a condition. You would have to differentiate between these two cases somehow - either by argument type, or some other parameter.
You can also use the data API to throw an exception if these methods are called for an object that has not been initialized with the list plugin. When ('xyz').list({ .. }) is first called, store some state variable in the data cache for that object. When any of the other methods - "list", "findItem", or "sort" are later invoked, check if the object contains that state variable in its data cache.
A better approach would be to namespace your plugin so that list() will return the extended object. The three extended methods can be called on its return value. The interface would be like:
$('selector').list({ ... });
$('selector').list().findOne(..);
$('selector').list().findAll(..);
$('selector').list().sort();
Or save a reference to the returned object the first time, and call methods on it directly.
var myList = $('selector').list({ ... });
myList.findOne(..);
myList.findAll(..);
myList.sort();
I found this solution here:
http://www.virgentech.com/blog/2009/10/building-object-oriented-jquery-plugin.html
This seems to do exactly what I need.
(function($) {
var TaskList = function(element, options)
{
var $elem = $(element);
var options = $.extend({
tasks: [],
folders: []
}, options || {});
this.changed = false;
this.selected = {};
$elem.sortable({
revert: true,
opacity: 0.5
});
this.findTask = function(test, look) {
var results = [];
for (var i = 0,l = options.tasks.length; i < l; i++)
{
var t = options['tasks'][i];
if (eval(test))
{
results.push(options.tasks[i]);
}
}
return results;
}
var debug = function(msg) {
if (window.console) {
console.log(msg);
}
}
}
$.fn.taskList = function(options)
{
return this.each(function() {
var element = $(this);
if (element.data('taskList')) { return; }
var taskList = new TaskList(this, options);
element.data('taskList', taskList);
});
}
})(jQuery);
Then I have
$('.task-list-table').taskList({
tasks: eval('(<?php echo mysql_real_escape_string(json_encode($tasks)); ?>)'),
folders: eval('(<?php echo mysql_real_escape_string(json_encode($folders)); ?>)')
});
var taskList = $('.task-list-table').data('taskList');
and I can use taskList.findTask(condition);
And since the constructor has $elem I can also edit the jQuery instance for methods like list(condition) etc. This works perfectly.
this.each isn't needed. This should do:
$.fn.list = function (options) {
this.find = function(test) {
//function logic
};
return this;
};
Note that you'd be overwriting jQuery's native find method, and doing so isn't recommended.
Also, for what it's worth, I don't think this is a good idea. jQuery instances are assumed to only have methods inherited from jQuery's prototype object, and as such I feel what you want to do would not be consistent with the generally accepted jQuery-plugin behaviour -- i.e. return the this object (the jQuery instance) unchanged.