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How to get Javascript object from HTML element

I have 3 "dice" objects created from this custom constructor:
function Dice() {
this.value = 0;
this.keep = false;
this.roll = function() {
this.value = Math.floor(Math.random()*6)+1;
};
}
Then, inside function rollOnce(), I have 3 HTML buttons inside a document.getElementById("paragraph1").innerHTML command that will display each dice's value as follows:
function rollOnce() {
(...)
document.getElementById("paragraph1").innerHTML =
'<button id="diceOne" class="unkept" onclick="keepDice(this.id)">'+dice1.value+'</button> ' +
'<button id="diceTwo" class="unkept" onclick="keepDice(this.id)">'+dice2.value+'</button> ' +
'<button id="diceThree" class="unkept" onclick="keepDice(this.id)">'+dice3.value+'</button> ';
}
Now, function keepDice(diceId) will set attribute class="kept" for each dice/button that has been clicked.
The next thing I want to do is to know which dice variable (dice1, dice2, dice3) has been clicked (in order to keep their value by doing diceN.keep = true;. Because after that there will be another round of the game in which only those dice which are "unkept" will get another diceN.roll() call. But my knowledge is still very limited and I only know how to access (HTML only) elements by using document.getElementsBy(...) (this is the HTML DOM, right? I'm currently learning this at W3Schools).
I have not yet learned about jQuery, AngularJS and all the other cool webdev stuff. So if it is possible to answer using only Javascript it would be much appreciated (even if other libs would make it easier! It's a bonus if there are alternative solutions and I would be happy to learn too!). Is this possible at all?
Thanks in advance,

Maybe something like class="kept-'+dice1.keet+'" onclick="keepDice(1)"
then
function keepDice(index){
dices[index].keep = true;
turns--;
if (turns > 0) {
rollOnce()
}
}

Try this:
function keepDice(id) {
var whichDice;
switch(id) {
case 'diceOne':
whichDice = dice1;
break;
case 'diceTwo':
whichDice = dice2;
break;
case 'diceThree':
whichDice = dice3;
break;
}
whichDice.keep = true;
}

If you stored your dice in an associative array like this:
dice['diceOne'] = new Dice();
dice['diceTwo'] = new Dice();
dice['diceThree'] = new Dice();
you would create the buttons almost the same way
<button id="diceOne" class="unkept" onclick="keepDice(this.id)">dice["diceOne"].value</button>
you could then write your dice function like this
function keepDice(id)
{
dice[id].keep = true;
document.GetElementById(id).setAttribute("class","kept");
//...
}

I came back to this again and realised there's a better way. It's quite a different approach than what you've got so far, but let me explain...
I know your question title is "How to get Javascript object from HTML element" but my answer better serves the question "How to get HTML element from Javascript object" and also better solves the problem you're facing.
First, I set the stage by creating a container element #paragraph1 and a "Roll Once" button which runs the rollOnce() function
<p id="paragraph1"></p>
<button onclick="rollOnce()">Roll Once</button>
Then I create the Dice() Object which takes a parameter - this parameter is the id of the element we wish to use as a container. We must wait for the HTML to load before we can find that container because until then, it simply doesn't exist yet. That's why I have bound a function to the document.onreadystatechange event.
So when the HTML has loaded and the document is ready, I initialise the Object, storing it in a var and the Object has all the required functions built-in for managing it's button.
function Dice(container) {
this.button = document.createElement("button");
this.button.innerHTML = 0;
document.getElementById(container).appendChild(this.button);
this.button.addEventListener('click', function() {
this.className = 'kept';
});
this.roll = function() {
if(this.button.className != 'kept') {
this.button.innerHTML = Math.floor(Math.random()*6)+1;
}
}
}
var dice1;
var dice2;
var dice3;
document.onreadystatechange = function () {
if(document.readyState == "complete") {
dice1 = new Dice("paragraph1");
dice2 = new Dice("paragraph1");
dice3 = new Dice("paragraph1");
rollOnce();
}
}
function rollOnce() {
dice1.roll();
dice2.roll();
dice3.roll();
}
Fully working demonstration is here: http://codepen.io/anon/pen/groEmg
Edit: If you want to get the values of the dice later, you can access the Objects' properties like so: dice1.button.innerHTML

You need to keep track of what has been kept and what has not been kept. It would be useful to hold all the dice functionality inside the dice class. every time you run rollOnce() you must also represent the kept/unkept state in the className.
Here's an example including what I gather is your current initialisation - define var dice then define rollOnce() then run rollOnce()
function Dice() {
this.value = 0;
this.kept = false;
this.roll = function() {
if(!this.kept) this.value = Math.floor(Math.random()*6)+1;
};
this.keep = function(id) {
this.kept = true;
document.getElementById(id).className = 'kept';
}
}
var dice1 = new Dice();
var dice2 = new Dice();
var dice3 = new Dice();
function rollOnce() {
dice1.roll();
dice2.roll();
dice3.roll();
document.getElementById("paragraph1").innerHTML =
'<button id="diceOne" class="'+(dice1.kept?'kept':'keep')+'" onclick="dice1.keep(\'diceOne\')">'+dice1.value+'</button> ' +
'<button id="diceTwo" class="'+(dice2.kept?'kept':'keep')+'" onclick="dice2.keep(\'diceTwo\')">'+dice2.value+'</button> ' +
'<button id="diceThree" class="'+(dice3.kept?'kept':'keep')+'" onclick="dice3.keep(\'diceThree\')">'+dice3.value+'</button> ';
}
rollOnce();
I've made it pass an ID to Dice.keep(id) just to have a live update of the DOM element which represents this Object variable.
Some clarification on the classnames since you're a beginner: I used ternary logic operators to quickly perform an IF THEN ELSE
So the part that says dice1.kept?'kept':'keep'
Actually means IF dice1.kept THEN 'kept' ELSE 'keep'
You can put a blank '' instead of 'keep' if you like since I don't think it's being used (but you might use it for CSS). Of course, there is plenty of room for improvement all over this code, but I wanted to keep it as similar to your sample code as possible. In fact, the first thing I would do is probably change the onclick to this: onclick="dice1.keep(this)" and then change your object like:
this.keep = function(button) {
this.kept = true;
button.className = 'kept';
}
http://codepen.io/anon/pen/MyrxyX
Edit: here's a slightly modified version where the Dice() object is agnostic to the DOM but still provides all the relevant data: http://codepen.io/anon/pen/MyrxbB

jQuery - add several textboxes

Im using this code:
jQuery.fn.update_textarea = function(test) {
$("#articles_textarea").html('');
for (i=0;i<test;++i) {
if (message[i]) { $("#articles_textarea").html('<textarea></textarea>'); }
else { message[i] = ''; $("#articles_textarea").html('<textarea></textarea>'); }
}
}
When im trying to add more then one, nothing happends but if i add 1 it works just as it should..
This is the "call"code
$("#articles_textarea").update_textarea(total);
This is variable total:
var total = parseFloat($(".testCounter").val()) + 5;
This is for calling only one textarea (the part that works):
$("#articles_textarea").update_textarea(1);
When i call one box it's working when i call several boxes nothing happends at all..

try with append method. .html() will remove the previous content
jQuery.fn.update_textarea = function(test) {
$("#articles_textarea").html('');
for (i=0;i<test;++i) {
if (message[i]) { $("#articles_textarea").append('<textarea></textarea>'); }
else { message[i] = ''; $("#articles_textarea").append('<textarea></textarea>'); }
}
}

Why you use jQuery.fn, when you don't use its functionality, whereas it works, only for the textareas with articles_textarea Id, you better do it using a simple function like:
function update_textarea(test) {
$("#articles_textarea").html('');
for (var i=0;i<test;++i) {
if (!message[i]){
message[i] = '';
}
$("#articles_textarea").append('<textarea></textarea>');
}
};
adding a new function to jQuery.fn is used to create new jQuery plugins, check this link for more info.
the other point was not using var i in your for loop which is not a good practice. Moreover both your if statement and the else, were the same, except message[i] = ''; part.
BTW if you want to do it using jQuery.fn, you better do it like:
jQuery.fn.update_textarea = function(test) {
this.html('');
for (var i=0;i<test;++i) {
if (!message[i]){
message[i] = '';
}
this.append('<textarea></textarea>');
}
};

JavaScript/jQuery variable scope in class (this)

I'm writing simple slider for my website. This slider contains list items. I want to use OOP approach.
My actual code:
var miniSlider = function(objId)
{
this.obj = $("#" + objId);
this.obj.settings = [];
this.obj.settings['items'] = $('ul li', this.obj).length;
this.pagerNext = this.obj.find("i.next");
this.pagerPrev = this.obj.find("i.prev");
this.pagerNext.on("click", function() {
alert(this.obj.settings['items']);
});
};
I can invoke a few other sliders (yes, that's why I introduced a class):
miniSlider("mini-slider");
The problem is that when I'm in jQuery this.pagerNext.on("click", function() { }); this is no longer my object but - it's become a clicked element. How can I access this.obj.settings after click in a well done way (and with multi sliders support)?
EDIT:
Here is a full code created with a cooperation with SOF community :)
var MiniSlider = function(objId)
{
this.obj = $("#" + objId);
this.obj.settings = {
items: $("ul li", this.obj).length,
autoChangeTime: 8000
};
this.obj.activeElement = null;
this.pagerNext = this.obj.find("i.next");
this.pagerPrev = this.obj.find("i.prev");
var self = this;
this.pagerNext.on("click", function() {
self.obj.activeElement = $('li.active', self.obj);
if(self.obj.settings.items > 0)
{
if(self.obj.activeElement.is(':last-child'))
{
$('li.active', self.obj).removeClass('active');
$('li', self.obj).first().addClass('active');
}
else
{
self.obj.activeElement.next().addClass('active').prev().removeClass('active');
}
}
});
this.pagerPrev.on("click", function()
{
self.obj.activeElement = $('li.active', self.obj);
if(self.obj.settings.items > 0)
{
if(self.obj.activeElement.is(':first-child'))
{
self.obj.activeElement.removeClass('active');
$('li', self.obj).last().addClass('active');
}
else
{
self.obj.activeElement.prev().addClass('active').next().removeClass('active');
}
}
});
this.obj.parent().on('mouseenter mouseleave', function(e) {
if (e.type == 'mouseenter')
{
$(this).addClass('stop');
}
else
{
$(this).removeClass('stop');
}
});
setInterval(function() {
if(self.obj.settings.items > 0 && !self.obj.parent().hasClass("stop"))
{
self.pagerNext.click();
}
}, this.obj.settings.autoChangeTime);
};
and invoke:
new MiniSlider("mini-slider");

Alex gave you the solution to the this problem in your callback, but there is another problem in your code.
You are calling the miniSlider() function without a new operator:
miniSlider("mini-slider");
That means that inside the function, this is not a unique object, but is actually the window object!
You need to use the new operator to create an individual object for each call:
new miniSlider("mini-slider");
But you should also change the name of this function to follow the JavaScript convention that constructors begin with a capital letter. Call it MiniSlider and use it like so:
new MiniSlider("mini-slider");
If you follow this convention (which most experienced JavaScript programmers do), it will help you remember when to use new. If the function begins with a capital letter, it's a constructor and you need to use new with it. Otherwise, you don't.
If you'd like to be able to use your constructor without new, that is also possible with a bit more code, e.g.:
function MiniSlider( objId ) {
if( this == window ) return new MiniSlider( objId );
// the rest of your constructor code goes here
}
But generally people don't bother with that and just use the initial capital letter on the constructor as a reminder to use new.
Also, as a suggestion, I like to use a meaningful name when I save this in a variable, and then I use that name consistently instead of using this at all. Doing it this way it might look like:
var miniSlider = function(objId) {
var slider = this;
slider.obj = $("#" + objId);
slider.obj.settings = [];
slider.obj.settings['items'] = $('ul li', slider.obj).length;
slider.pagerNext = slider.obj.find("i.next");
slider.pagerPrev = slider.obj.find("i.prev");
slider.pagerNext.on("click", function() {
alert(slider.obj.settings['items']);
});
};
Why do I prefer that approach over using this in most places and another variable like self where you need it? This way I don't have to remember which to use: I can always use slider in the code instead of this. (Of course you could use self or any other name; I just like to have a more meaningful name if I'm going to the trouble of making up a name at all.)
Another minor problem in the code is in these two statements:
slider.obj.settings = [];
slider.obj.settings['items'] = $('ul li', slider.obj).length;
You shouldn't use an Array when you are going to be giving it named properties like this. Use an Object instead. Arrays should only be used when you have numeric indexes like 0, 1, 2, etc. And with an object literal you can set the property at the same time:
slider.obj.settings = {
items: $('ul li', slider.obj).length
};
Also, when you use that property:
alert(slider.obj.settings['items']);
you can write it more simply as:
alert(slider.obj.settings.items);
Either way it does the same thing.

Save a reference to this in a local variable, and use that variable instead of this in the nested function.
var self = this;
this.pagerNext.on("click", function() {
alert(self.obj.settings['items']);
});

How to store variables: Privileged method, static property

Instead of just saying:
var thing = timeConsumingMethod();
I have my variable hidden in a method like so:
function _thing() {
var thing = timeConsumingMethod() );
return thing;
}
It gets called a number of times. I'm concerned that I'm made things very inefficient. I assume it calls timeConsumingMethod every time (which is unneeded, it's always the same) I call "_thing()" to get my variable.
How do I manage these types of variables in simple efficient way? Is something like this a solution?:
function _thing() {
return _thing.thing
}
_thing.thing = timeConsumingMethod();
Basically, i want the protection of a function and to (ideally0 access my variable using _thing() or something similar, but I only want timeConsumingMethod to run once.
edit: tried this, doesn't work either:
function _thingy() {
var thing = timeConsumingMethod();
}
_thingy.test = function() {
return( _thingy.thing)
}

Why not just:
function SomethingTimeConsuming() { ... }
function LazyThing(sourceFunction) {
this.sourceFunction = sourceFunction;
this.value = null;
this.Value = function() {
if ( this.value == null) this.value = sourceFunction();
return this.value;
}
}
JSFiddle: http://jsfiddle.net/YSAjJ/
Output:
[14:20:20.079] Calling time-consuming function *(1 time)

Is there a Javascript equivalent of Ruby's andand?

In trying to make my Javascript unobtrusive, I'm using onLoads to add functionality to <input>s and such. With Dojo, this looks something like:
var coolInput = dojo.byId('cool_input');
if(coolInput) {
dojo.addOnLoad(function() {
coolInput.onkeyup = function() { ... };
});
}
Or, approximately equivalently:
dojo.addOnLoad(function() {
dojo.forEach(dojo.query('#cool_input'), function(elt) {
elt.onkeyup = function() { ... };
});
});
Has anyone written an implementation of Ruby's andand so that I could do the following?
dojo.addOnLoad(function() {
// the input's onkeyup is set iff the input exists
dojo.byId('cool_input').andand().onkeyup = function() { ... };
});
or
dojo.byId('cool_input').andand(function(elt) {
// this function gets called with elt = the input iff it exists
dojo.addOnLoad(function() {
elt.onkeyup = function() { ... };
});
});

I don't know Dojo, but shouldn't your first example read
dojo.addOnLoad(function() {
var coolInput = dojo.byId('cool_input');
if(coolInput)
coolInput.onkeyup = function() { ... };
});
Otherwise, you might end up trying to access the element before the DOM has been built.
Back to your question: In JavaScript, I'd implement andand() as
function andand(obj, func, args) {
return obj && func.apply(obj, args || []);
}
Your example could then be written as
dojo.addOnLoad(function() {
andand(dojo.byId('cool_input'), function() {
this.onkeyup = function() { ... };
});
});
which isn't really that much shorter than using the explicit if statement - so why bother?

The exact syntax you want is not possible in JavaScript. The way JavaScript executes would need to change in a pretty fundamental fashion. For example:
var name = getUserById(id).andand().name;
// ^
// |-------------------------------
// if getUserById returns null, execution MUST stop here |
// otherwise, you'll get a "null is not an object" exception
However, JavaScript doesn't work that way. It simply doesn't.
The following line performs almost exactly what you want.
var name = (var user = getUserById(id)) ? user.name : null;
But readability won't scale to larger examples. For example:
// this is what you want to see
var initial = getUserById(id).andand().name.andand()[0];
// this is the best that JavaScript can do
var initial = (var name = (var user = getUserById(id)) ? user.name : null) ? name[0] : null;
And there is the side-effect of those unnecessary variables. I use those variables to avoid the double lookup. The variables are mucking up the context, and if that's a huge deal, you can use anonymous functions:
var name = (function() {return (var user = getUserById(id)) ? user.name : null;})();
Now, the user variable is cleaned-up properly, and everybody's happy. But wow! what a lot of typing! :)

You want dojo.behavior.
dojo.behavior.add({
'#cool_input': {
onKeyUp: function(evt) { ... }
}
});

How about something like this:
function andand(elt, f) {
if (elt)
return f(elt);
return null;
}
Call like this:
andand(dojo.byId('cool_input'), function(elt) {
// this function gets called with elt = the input iff it exists
dojo.addOnLoad(function() {
elt.onkeyup = function() { ... };
});
});

As far as I know there isn't a built-in JavaScript function that has that same functionality. I think the best solution though is to query by class instead of id and use dojo.forEach(...) as you will be guaranteed a non-null element in the forEach closure.
You could always use the JavaScript equivalent:
dojo.byId('cool_input') && dojo.byId('cool_input').whateverYouWantToDo(...);

I've never used dojo, but most javascript frameworks (when dealing with the DOM) return the calling element when a method is called from the element object (poor wording, sorry). So andand() would be implicit.
dojo.addOnLoad(function() {
dojo.byId('cool_input').onkeyup(function(evt) { /*event handler code*/
});
});

For a list:
Array.prototype.andand = function(property, fn) {
if (this.filter(property).length > 0) this.map(fn);
}