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Javascript: Chaining on elements like jQuery

I'm trying to replicate jQuery's element manipulation to a certain extent. Now what I have found to be very useful is the .first() selector. I would like to be able to chain functions like this;
getElement(selector).first().hasClass(className);
Now, there are 2 issues with how far I've gotten (Do note that my code example is minimised, so please, no comments about error-handling.)
var getElement = function(selector, parent) {
ret = document.querySelectorAll(selector);
this.element = ret;
this.hasClass = function(className) {
className.replace('.', '');
if(this.multiple())
{
console.log('Cannot use hasClass function on multiple elements');
return false;
}
};
this.first = function() {
this.element = this.element[0];
return this;
};
return this;
};
My current problem
If I call my function;
var $test = getElement('.something');
//result: nodelist with .something divs
If I call for the first element within the result;
$test.first();
//Result: First div, perfect!
However, now if I call $test again, it will replace the elements property with the result of first(), meaning I have "lost" my old values. I don't want to lose them, I only want the first() functions for that specific functionality. Then I want $test to return all elements again.
Also, recalling first() will now end up undefined, since there is only 1 element left within this as it has deleted the old elements from within the object.
Another attempt
Now, I've also tried to turn it around a bit by returning the first-child instead of the entire class object;
this.first = function() {
return this.element[0];
};
However, I will
$test.first().hasClass(className);
//Returns ERROR, method hasClass undefined
this is because .hasClass exists on the original this, which doesn't get returned anymore since I'm now returning the element.
I have tried to get something out of jQuery's library, though that just confused me more...
I have googled this subject, but with all the 'chaining methods' solutions I'm finding, all of them seem to be overwriting the original values of the object, which is not what I want to happen. One other solution actually required me to re-initiate the object over and over again, which did not seem very efficient to me... Any help is appreciated. I'm assuming I'm going about this completely the wrong way.
-- If you can help me, please do explain why your solution works. I really feel like if I understand this, my understanding of javascript can expand a lot further. I just need to get past this structural(?) issue.

A method like first() should not modify this, it should create a new object and return that. You only use return this; in methods that modify an element rather than returning information derived from the element.
this.first = function() {
return new getElement(this.element[0]);
};
And note that you have to use new getElement to create an object, not just getElement.
This also requires a change to the constructor, so it can accept either a selector string or an element:
var getElement = function(selector, parent) {
var ret = typeof selector == "string" ? document.querySelectorAll(selector) : [selector];
...
}
You should also consider doing this in proper OO fashion, by putting the methods in a prototype, rather than defining them in every object.
var getElement = function(selector, parent) {
var ret = typeof selector == "string" ? document.querySelectorAll(selector) : [selector];
this.element = ret;
};
getElement.prototype.hasClass = function(className) {
className.replace('.', '');
if (this.multiple()) {
console.log('Cannot use hasClass function on multiple elements');
return false;
}
};
getElement.prototype.first = function() {
return new getElement(this.element[0])
};

this in your outer function refers to the window / global object.
Instead, return the ret variable itself.
In the inner functions (which become the object's methods), this acts the way you expect it to.
Here's an alternative solution, which allows chaining, even after you've called the first method:
var getElement = function(selector, parent) {
var ret = typeof selector == 'string' ? document.querySelectorAll(selector)
: selector;
ret.hasClass = function(className) {
if(!this.classList) {
console.log('Cannot use hasClass function on multiple elements');
return false;
} else {
return this.classList.contains(className);
}
};
ret.first = function() {
return new getElement(this[0]);
};
return ret;
};
console.log(getElement('p').length); //2
console.log(getElement('p').first().innerHTML); //abc
console.log(getElement('p').first().hasClass('test')); //true
console.log(getElement('p').first().hasClass('nope')); //fase
console.log(getElement('p').hasClass('test')); //false (multiple elements)
<p class="test">
abc
</p>
<p>
def
</p>

Here is how I would approach this:
Create a constructor, say Search, tasked to find the elements based on the input. Using a constructor is proper OO Programming and you also have the advantage of defining methods once in the prototype and they can be accessed by all instances.
Ensure that the context (this) is an array-like object, with numeric properties and a length, so that you can easily iterate over every matched element in the traditional way (using for loops, [].forEach etc).
Create a function, say getElement, that will use the constructor and return the result without having to use the new keyword all the time. Since the function returns an instance of our constructor, you can chain the methods you want as you would normally do.
The method first uses the constructor to create a new instance instead of modifying the original, since its role is to return the first element, not delete everything but the first element.
Each time you come up with a new method you want your object to have, you can simply add it to the prototype of the constructor.
Snippet:
;(function () {
function Search (value) {
var elements = [];
/* Check whether the value is a string or an HTML element. */
if (typeof value == "string") {
/* Save the selector to the context and use it to get the elements. */
this.selector = value;
elements = document.querySelectorAll(value);
}
else if (value instanceof Element) elements.push(value);
/* Give a length to the context. */
this.length = elements.length;
/* Iterate over every element and inject it to the context. */
for (var i = 0, l = this.length; i < l; i++) this[i] = elements[i];
}
/* The method that returns the first element in a Search instance. */
Object.defineProperty(Search.prototype, "first", {
value: function () {
return new Search(this[0]);
}
});
/* The global function that uses the Search constructor to fetch the elements. */
window.getElement = (value) => new Search(value);
/* Create a reference to the prototype of the constructor for easy access. */
window.getElement.fn = Search.prototype;
})();
/* Get all elements matching the class, the first one, and the first's plain form. */
console.log(getElement(".cls1"));
console.log(getElement(".cls1").first());
console.log(getElement(".cls1").first()[0]);
/* ----- CSS ----- */
.as-console-wrapper {
max-height: 100%!important;
}
<!----- HTML ----->
<div id = "a1" class = "cls1"></div>
<div id = "a2" class = "cls1"></div>
<div id = "a3" class = "cls1"></div>
Example:
In this example, I'm adding a new method called hasClass to the prototype of the constructor.
/* The method that returns whether the first element has a given class. */
Object.defineProperty(getElement.fn, "hasClass", {
value: function (value) {
return this[0].classList.contains(value);
}
});
/* Check whether the first element has the 'cls2' class. */
console.log(getElement(".cls1").first().hasClass("cls2"));
<!----- HTML ----->
<script src="//pastebin.com/raw/e0TM5aYC"></script>
<div id = "a1" class = "cls1 cls2"></div>
<div id = "a2" class = "cls1"></div>
<div id = "a3" class = "cls1"></div>

I think the easiest would be to return a new class that contains the nodes you have selected. That would be the easiest solution, as you don't really want to mutate any of your previous selectors.
I made a small example, using some ES6 that makes a few things easier to work with, which also has a $ to initiate the selections being made.
You would notice that first of all, any selection that is made, is just calling the native document.querySelectorAll but returns a new Node class. Both first and last methods also return those elements.
Lastly, hasClass should work on all elements in the current nodes selections, so it will iterate the current node, and check all classes in there, this one returns a simple bool, so you cannot continue with the method chaining there.
Any method you wish to chain, should either:
return this object (the current node)
return an element of the this object as a new node so any further manipulations can be done there
const $ = (function(global) {
class Node extends Array {
constructor( ...nodes ) {
super();
nodes.forEach( (node, key) => {
this[key] = node;
});
this.length = nodes.length;
}
first() {
return new Node( this[0] );
}
last() {
return new Node( this[this.length-1] );
}
hasClass( ...classes ) {
const set = classes.reduce( (current, cls) => {
current[cls] = true;
return current;
}, {} );
for (let el of this) {
for (let cls of el.classList) {
if (set[cls]) {
return true;
}
}
}
return false;
}
}
global.$ = function( selector ) {
return new Node( ...document.querySelectorAll( selector ) );
};
return global.$;
}(window));
let selector = $('.foo');
let first = selector.first(); // expect 1
console.log(first[0].innerHTML);
let last = selector.last();
console.log(last[0].innerHTML); // expect 4
console.log( first.hasClass('foo') ); // expect true
console.log( first.hasClass('bar') ); // expect false
console.log( selector.hasClass('foo') ); // expect true
console.log( selector.hasClass('bar') ); // expect true
<div class="foo">1</div>
<div class="foo">2</div>
<div class="foo bar">3</div>
<div class="foo">4</div>

You can update getElement so it returns back again when you send it an element.
var getElement = function(selector, parent) {
var ret = null
if (typeof selector === "string") {
ret = document.querySelectorAll(selector);
} else {
ret = selector
}
this.element = ret;
this.hasClass = function(className) {
className.replace('.', '');
if (this.multiple()) {
console.log('Cannot use hasClass function on multiple elements');
return false;
}
};
this.first = function() {
this.element = getElement(this.element[0]);
return this;
};
return this;
};
var test = getElement(".foo");
console.log(test.first())
console.log(test.first().hasClass)
<div class="foo">1</div>
<div class="foo">2</div>
<div class="foo">3</div>
<div class="foo">4</div>

You can use .querySelectorAll(), spread element and Array.prototype.find(), which returns the first match within an array or undefined
const getElement = (selector = "", {prop = "", value = "", first = false} = {}) => {
const el = [...document.querySelectorAll(selector)];
if (first) return el.find(({[prop]:match}) => match && match === value)
else return el;
};
let first = getElement("span", {prop: "className", value: "abc", first: true});
console.log(first);
let last = getElement("span");
console.log(all);
<span class="abc">123</span>
<span class="abc">456</span>

How to return different values

How Jquery can chain and return multiple values?
I know you can chain:
const $ = {
a() {
return this;
}
b() {
return this;
}
}
$.a().b()
The example below will speaks by itself:
$('div').find('p').hide().css() // find an apply style
$('div').find('p') // return all the "p"
See my example
How jQuery return all the p and keep the plugin instance?
How can I achieve the same behavior?
How to know if there is another call after find()?
Thanks.

All of these API members are returning a jQuery object. It just so happens that the jQuery API has all of these members on it. That is how you are able to chain calls on the same object.
Taking a look at the docs:
In API calls that return jQuery, the value returned will be the original jQuery object unless otherwise documented by that AP
show() returns a jQuery type
hide() returns a jQuery type
find() returns a jQuery type
Note that css() doesn't return a jQuery type, so you can't chain off that.

jQuery follows an approach like this one:
function $(param) {
if(!(this instanceof $)) // if $ is called without using 'new'
return new $(param); // then return a new instance
this.param = param; // ...
}
$.prototype.a = function() { // the function a has to...
// a's logic
console.log("this is a");
return this; // return this so there will be chaining
}
$.prototype.b = function() { // the same goes for b
// b's logic
console.log("this is b");
return this;
}
$.c = function() {
// c's logic
console.log(c);
// not returning this as c can't be chained
}
$("some param").a().b().a();
In the example, a and b are methods (attached to the prototype) that return this so they can be chained (example of $(...).val(), $(...).addClass()). c however is attached as a property to the function object $ directly, thus it can't be chained (example of $.isArray() and $.each() not to be confused with $(...).each()).
A mini-jQuery example:
function $(selector) {
if(!(this instanceof $))
return new $(selector);
if(selector instanceof $) // if selector is already an instance of $ then just return it to be used as it is
return selector;
else if(typeof selector === "string") // otherwise, if selector is a string, then select the elements
this.elems = document.querySelectorAll(selector);
else if($.isArray(selector)) // otherwise, if the selector is an array, then the elements will be those in the array ( this is used by find )
this.elems = selector;
else if(!selector) // otherwise, selector is a DOM element
this.elems = [selector];
}
$.prototype.each = function(callback) { // take a function (callback) and call it on all elements
for(var i = 0; i < this.elems.length; i++) // for each element in this.elems
callback.call(this.elems[i], i, this.elems[i]); // call callback, setting its this to the current element and passing to it two parameters: the index and the element itself
return this;
}
$.prototype.css = function(prop, value) { // a function that take a CSS property and probably a value and either set or return the value of that CSS property
if(value === undefined) // if the value is not provided, then
return this.elems[0].style[prop]; // return the value of the first element in the selection (some checking if the element exist should be here)
return this.each(function() { // if a value is provided, then
this.style[prop] = value; // set the style of each element in the selection, and then return this (this.each returns this so just return this.each())
});
}
$.prototype.text = function(val) { // follows the same as css above
if(val === undefined)
return this.elems[0].textContent;
return this.each(function() {
this.textContent = val;
});
}
$.isArray = function(obj) { // is not a method (this is not the instance of the class)
return Object.prototype.toString.call(obj) === "[object Array]";
}
// FIND:
$.prototype.find = function(selector) {
var newElems = []; // the array of new elements
this.each(function() { // for each element in the current selection
var thisElems = this.querySelectorAll(selector); // select it descendants that match the selector
for(var i = 0; i < thisElems.length; i++) // add them to the result array
newElems.push(thisElems[i]);
});
// remove duplicates // this is important as elements could be selected twice (elements inside a parent inside a grand parent where both parent and grand parent are in the old selection), check jQuery's source code for how they remove duplicats using sort
return $(newElems); // return a new $ object using the new array of elements as the wrapped elements (check the constructor for more informations)
}
// usage:
$("div").css("background", "#fd8") // selects all divs and change their background
.find("span") // now find all spans inside those divs
.css("background", "#0ff"); // change their background
<div>a</div>
<div class="even"><span>b</span></div>
<div>c</div>
<div class="even">d</div>
<div><span>e</span></div>
<span>outer span</span>

I try to write the java script code like oops how to extend the DOM elements?

In my code like ,
function ElementBase(name) {
this.tagName = typeof name != "" ? name : 'div';
this.createElem();
}
ElementBase.prototype = {
createElem: function() {
this.elem = document.createElement(this.tagName);
},
getIndex: function() {
var nodes = this.elem.parentNode.childNodes,
node;
var i = count = 0;
while ((node = nodes.item(i++)) && node != this.elem)
if (node.nodeType == 1) count++;
return (count);
}
};
I try to create the DOM element tag is "div".
function Div() {
this.tagName = 'div'
ElementBase.call(this, this.tagName);
}
Div.prototype = Object.create(ElementBase.prototype);
My Question is,
1) How to access the getIndex function from the html document after inserting the created objects?
example:
var div = new Div();
div.id = "d1"
document.body.appendChild(div.elem);
// After div.getIndex() working
Then some situation i need the index value of that div (id="d1") element from document.
var d= document.getElementById("d1");
d.getIndex() //not working
What mistakes i did it in above code?
thanks advance..

I think when you do document.body.appendChild(div.elem) you just do document.body.appendChild(document.createElement('div')) nothing more.
And when you do var d= document.getElementById("d1"); d is just an object return from the DOM that has nothing to do with your var div
what you can do is:
Div.prototype.getIndex.call(d);
But that doesn't actually extend your object. Actually extending a DOM object is a bad practice (check this http://perfectionkills.com/whats-wrong-with-extending-the-dom/).

Look closely at your code.
div is an instance of Div and it has a property .elem that holds the actual DOM element.
So when you do div.id = "d1", you are not setting the id of the DOM element.
var div = new Div();
div.id = 'd1'; // <div></div>
div.elem.id = 'd1'; // <div id="d1"></div>
But there's one more problem: when you do d= document.getElementById("d1"), what you get is a DOM element, not an instance of Div().
Since .getIndex() is defined on .prototype of Div(), plain old DOM elements don't have access to it.
How you solve this situation depends on what exactly you need to accomplish with your code.
Edit 1: In response to OP's comment:
document.getElementById() returns an instance of HTMLDivElement, which is fundamentally different from an instance of Div.
One solution is to use a setter method:
function Div() {
// ...
}
Div.prototype.setId = function setId(id) {
this.elem.id = id;
}
var div = new Div();
div.setId('d1'); // same as doing div.elem.id = 'd1';
another solution is to use id in the constructor function itself:
function Div(id) {
// ...
this.elem.id = id; // or you can use "this.setId(id)"
/*
if "id" is provided,
it will take that value,
else it is set to "undefined",
which is the same as not being set
*/
}
Div.prototype.setId = function setId(id) {
this.elem.id = id;
}
var div = new Div('d1'); // same as doing div.elem.id = 'd1';
div.setId('d2'); // same as doing div.elem.id = 'd2';

Select parent object from a field in js

I am relatively new to OOP so I am not sure about the terminology.
I have created a DOM element as a field of an object (eg myObject.myElement) and I appended the element to the document. The object has a .mousemove() event attached (using jQuery). I want to be able to select the object (myObject) for whom the selected element (myElement) is a field so that I can access other fields of the object. There is more than one object and the event handler is the same for elements of different objects. Is it possible to select the parent object of the element? Do I need to give the element the same fields so that I can access the same data?
I want to be able to do something like this but maybe it is not that straightforward:
$('.bubble').on({mousemove: function () {
parentObject = this.parentObject();
alert(parentObject.otherDataField);
});
The element was created like this:
function bubbleObject(value)
{
this.value = value;
this.element = document.createElement('div');
$(this.element).appendTo('.bubbles');
}
myFirstBubble = new bubbleObject(10);
mySecondBubble = new bubbleObject(100);
and I need to be able to access the value field for the object (I am making it simpler as the code is pretty long and mostly irrelevant to my issue).
Do I need to do this:
function bubbleObject(value)
{
this.value = value;
this.element = document.createElement('div');
$(this.element).appendTo('.bubbles');
this.element.value = value; // add same value to element
}
or is there a better way?

A back reference to the parent could be better than copying values:
function bubbleObject(value)
{
this.value = value;
this.element = document.createElement('div');
$(this.element).appendTo('.bubbles');
this.element.parent = this;
}
However, using this way you have to use element.parent.value instead.

Another approach (as I mentioned before) is to scan all element-containing objects if they contain a specific element. If you don't have all these objects in an array you have to scan all window components (as I said, this is expensive):
function findElement(element) {
for (obj in window) {
if (typeof obj === 'object' && obj.myElement == element) {
return obj;
}
}
return null;
}
This is just an untested draft. And it would be so much better if you have a list of parent objects which you can use instead of window.
function findElement(element) {
for (int i = 0, l = objList.length; i < l; i++) {
if (typeof objList[i] === 'object' && objList[i].myElement == element) {
return objList[i];
}
}
return null;
}

How to check for a JavaScript Object given it's name as a string?

I'm having trouble figuring out how I can take a string of an object name and check if that object actually exists.
What I'm trying to accomplish is have an array the defines the required objects for a particular JavaScript "module" to work, for instance:
var requiredImports = ['MyApp.Object1', 'MyApp.Object2'];
Then using requiredImports, I want to loop over them and check if the are defined. Without using the above array, I can do the following which is what I'm trying to accomplish:
if (MyApp.Object1 == undefined) {
alert('Missing MyApp.Object1');
}
But using the above, I'd have to hard code this for every module rather than making a generic method that I can just pass it an array of strings and have it effectively do the same check for me.
I tried doing this by just passing it the objects themselves such as:
var requiredImports = [MyApp.Object1, MyApp.Object2];
But that throws a JavaScript error when those objects do not exist, which is what I'm trying to catch.

var MyApp = {
Object1: {}
};
function exists(varName, scope) {
var parent = scope || window;
try {
varName.split('.').forEach(function (name) {
if (parent[name] === undefined) {
throw 'undefined';
}
parent = parent[name];
});
}
catch (ex) {
return false;
}
return true;
}
console.log(
exists('MyApp.Object1'), // true
exists('MyApp.Object2'), // false
exists('window'), // true
exists('document'), // true
exists('window.document') // true
);
// or
console.log(
['MyApp.Object1', 'MyApp.Object2', 'window', 'document', 'window.document'].filter(function (varName) {
return !exists(varName);
})
);
// => ["MyApp.Object2"]
Note: that forEach is ES5 and as such not implemented in some browsers. But if you'd go with this solution, there is a nice polyfill here.

You can check for definedness with
if ( typeof window['MyApp'] === 'undefined' ||
typeof window['MyApp']['Object1'] === 'undefined' )
{
alert('Missing MyApp.Object1');
}
and so on.

Assuming MyApp.Object1 is a global scope, window is the parent object and since that is the top level object, you don't need to prefix your global vars with it. So window.MyApp.Object1 is the same as MyApp.Object1 (again, assuming this is within global scope).
Also, in javascript, MyApp['Object1'] is the same as MyApp.Object1. So if we apply this principle to the main window object, you can check for window['MyApp'] or window['MyApp']['Object1'] and the key here is that you can replace 'MyApp' and 'Object1' with a variable.
Example:
/* check if a variable/object exists in the global scope) */
function checkIfExists(someVar) {
if (typeof(window[someVar]) == 'undefined')
return true;
return false;
}
var foo = 'bar';
alert(checkIfExists('foo'));

You can evaluate your custom expression in JavaScript. Consider the code below:
var MyApp = {
Object1: "foo",
Object2: "bar"
};
var IsExists = function(varName) {
return new Function('return typeof(' + varName + ') === "undefined" ? false : true;')();
};
USAGE
var requiredImports = ['MyApp.Object1', 'MyApp.Object2'];
for (var i = 0; i < requiredImports.length; i++)
{
alert(requiredImports[i] + ": " + IsExists(requiredImports[i]))
}

You only get error for first level (MyApp in your example). I assume you have only a few first-level requires, so check them manually by window[x] which does not throw:
var requiredTopLevel = ['MyApp'];
for (var i = 0; i < requiredTopLevel.length; ++i) {
if ("undefined" === typeof window[requiredTopLevel[i]]) {
// problem with requiredTopLevel[i]
}
}
and then, to check nested requires (if top-level is present) you can use the values without fear. For example this will work:
var requiredNested = { 'Object1':MyApp.Object1, 'Object2':Myapp.Object2 };
for (var name in requiredNested) {
if ("undefined" === typeof requiredNested[name]) {
// problem with name
}
}