We Keep Coding

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 Not Defined within a function

Alright, here's a puzzler. I've got a jQuery function to display a PHP generated list of announcements for a website via .fadeIn/.fadeOut; the very first thing loaded on the page is jQuery 1.11.xx from a CDN. I'm running Bootstrap, fullCalendar, SmartMenus, etc., and jQuery is most definitely loading.
Except within the setInterval() to update the announcement. This is rough-code, some functionality isn't present, but to my mind it should be doing an animation.
var announcementArray = [];
var announcementSource = "../announcements.php";
var totalAnnc;
$.getJSON(announcementSource, function(data) {
announcementArray = data.concat();
totalAnnc = announcementArray.length;
});
var count = 0;
var fadeAnnc = function() {
$('#announcementArea').text(announcementArray[count].announceText);
$('#announcementArea').fadeIn('slow',function() {
$('#announcementArea').css('display','block');
}).delay(2000).fadeOut('slow',function() {
count = (count + 1) % totalAnnc;
});
};
setInterval(function() {
fadeAnnc();
}, 3000);
Instead, when I run the page, I get a "function not defined" error for any jQuery function that's called within the setInterval(). If I call using document.getElementById('announcementArea').innerHTML = etc., it works, but doing the fade in/out via DOM manipulation seems to be more work than is needed when jQuery is available and working everywhere else on the page.
I've tried a few scope adjustments and have been working on what should be simple code for the last 5 hours. So, where's my glaring error? ;)

Not sure what kind of scope issue you are having (looks like it's the result of unposted code, as everything in your question looks OK), but if you want a fairly foolproof way of passing along the jQuery object, you could always pass it as a parameter:
var fadeAnnc = function($) {
$('#announcementArea').text(announcementArray[count].announceText);
$('#announcementArea').fadeIn('slow',function() {
$('#announcementArea').css('display','block');
}).delay(2000).fadeOut('slow',function() {
count = (count + 1) % totalAnnc;
});
};
setInterval(function() {
fadeAnnc($);
}, 3000);
Based on your updated answer, here's another possible solution:
(function($){
var announcementArray = [];
var announcementSource = "../announcements.php";
var announcementSpace = "#announcementArea";
$.getJSON(announcementSource, function(data) {
announcementArray = data.concat();
if (announcementArray.length === 0) {
$('#anncRow').css('display','none');
}
});
var count = 0;
var masterCount = 0;
var totalAnnc = announcementArray.length;
var timer;
var fadeAnnc = function() {
if (announcementArray.length > 0) {
$(announcementSpace).html(announcementArray[count].announceText);
$(announcementSpace).fadeIn(750, function() {
$(announcementSpace).css('display','block');
}).delay(4500).fadeOut(750, function() {
$(announcementSpace).css('display','hidden');
});
}
count += 1;
if ((count % announcementArray.length) == 0) {count = 0}
};
setInterval(fadeAnnc, 6000);
}(jQuery));
$ is defined as a function parameter and thus overrides the globally scoped $ within the function body, protecting it's definition for your code. This is actually exactly what jQuery recommends when creating an extension.

My previous answer - scratch that:
The issue was more interesting - somewhere between the SmartMenu plugin and the LibraryThing book display widget there is a jQuery conflict created. This explains why - depending on the load order - different parts would break, but always the setInterval(), which always loaded after SmartMenu and LibraryThing.
So, my somewhat messy solution is to release the $ at the beginning of the script and reclaim it at the end so on other pages jQuery has access to it, like so:
jq = jQuery.noConflict();
var announcementArray = [];
var announcementSource = "../announcements.php";
var announcementSpace = "#announcementArea";
jq.getJSON(announcementSource, function(data) {
announcementArray = data.concat();
if (announcementArray.length === 0) {
jq('#anncRow').css('display','none');
}
});
var count = 0;
var masterCount = 0;
var totalAnnc = announcementArray.length;
var timer;
var fadeAnnc = function() {
if (announcementArray.length > 0) {
jq(announcementSpace).html(announcementArray[count].announceText);
jq(announcementSpace).fadeIn(750, function() {
jq(announcementSpace).css('display','block');
}).delay(4500).fadeOut(750, function() {
jq(announcementSpace).css('display','hidden');
});
}
count += 1;
if ((count % announcementArray.length) == 0) {count = 0}
};
setInterval(fadeAnnc, 6000);
$ = jQuery.noConflict();

Use closures (which is considered good practice anyways):
(function($) {
var your_function = function() {
$(...);
};
setTimeout(function() {
your_function();
});
}(jQuery));
Using closures creates a sort of 'sandbox' for your code, so you don't have to worry about overwriting any variables declared in a parent scope (such as the dollar-sign $ used by jQuery).

Javascript reference in loop: "Uncaught TypeError: Cannot read property 'value' of undefined"

I tried debugging my code for like a few hour but I got nothing out of it. The issue is that it makes absolutely no sense on why it reports an error every time I tried to use document.forms[0][i] (i as the iterator) in the event listener but "this" satisfies the code.
//broken
var addListeners = function() {
var i;
var formFields = document.forms[0];
var formSubmit = formFields["submit"];
for (i = 0; i < formFields.length; i++) {
if (formFields[i] != formSubmit) {
formFields[i].onblur = (function () {
checkNonEmpty(formFields[i]);
});
}
}
};
//works
var addListeners = function() {
var i;
var formFields = document.forms[0];
var formSubmit = formFields["submit"];
for (i = 0; i < formFields.length; i++) {
if (formFields[i] != formSubmit) {
formFields[i].onblur = (function () {
checkNonEmpty(this);
});
}
}
};
Wouldn't "this" refer to document.forms[0][i]?... formFields references to document.forms[0]. However the exact same code (with "this" where formFields[i] is at) works just fine.
Here is the demo: http://jsfiddle.net/PbHwy/

Cranio's answer already contains the root of the matter. To get rid of this you can either include formFields[i] by using closures
var blurCallbackGenerator = function(element){
return function () {
checkNonEmpty(element);
};
};
formFields[i].onblur = blurCallbackGenerator(formFields[i]);
/* // dense version:
formFields[i].onblur = (function(element){
return function () {
checkNonEmpty(element);
};
})(formFields[i]);
*/
or simply using this.
See also:
MDN: Creating closures in loops: A common mistake

Because you define formFields in a scope outside (or better, different than) the event listener. When the event listener is called, it is called not in the addListeners function where you define formFields, but "independently", so the reference is lost and its value is undefined (but this works because it is not dependent on that scope).

The problem is that the variable i (referred to in each of your handlers) is the exact same variable in each of them, which by the time the loop has finished has value formFields.length+1 and is therefore wrong for all of them. Try this instead [note: the below used to say something VERY WRONG before I edited it -- thanks to Zeta for pointing out my mistake]:
var addListeners = function() {
var i;
var formFields = document.forms[0];
var formSubmit = formFields["submit"];
for (i = 0; i < formFields.length; i++) {
if (formFields[i] != formSubmit) {
formFields[i].onblur = (function(j) {
return (function () {
checkNonEmpty(formFields[j]);
})(i);
});
}
}
};
and you'll find it works (unless there's another bug that I haven't noticed).
If you can afford to support only Javascript 1.7 and above, you can instead write your old code but make your for look like this: for (let i=0; i<formFields.length; i++). But you quite possibly can't.

Speed test: while() cycle vs. jQuery's each() function

I have an array of objects called targets and I want to execute a function on each of those objects. The first method:
targets.each(function() {
if (needScrollbars($(this))) {
wrap($(this), id);
id = id + 1;
}
});
This method gives execution speed of ~125ms. The second method is:
var i=0;
while (targets[i] != undefined) {
if (needScrollbars($(this))) {
wrap($(this), id);
id = id + 1;
}
i = i+1;
}
This second method takes whopping 1385ms to execute and I get my head around that. Does anyone have any idea why a bare bones cycle runs slower than a function which I'm only guessing that's doing (just guessing) a whole lot more than a simple cycle?
Thank you.

They are totally different. The this in the first example is the current target, in the second example this is the "external" this. You should change the second example as:
var i=0;
while (targets[i] != undefined) {
var cur = $(targets[i]);
if (needScrollbars(cur)) {
wrap(cur, id);
id = id + 1;
}
i = i+1;
}
The relevant quote
More importantly, the callback is fired in the context of the current DOM element, so the keyword this refers to the element.
But I don't know why you haven't written as:
for (var i = 0; i < targets.length; i++)
{
var cur = $(targets[i]);
if (needScrollbars(cur)) {
wrap(cur, id);
id = id + 1;
}
}
And in the end the each "method" is easier to comprehend (for me).

Your second method is not functionally equivalent to the first one.
Why? Because it uses this, making it a closure on the global scope. Of course the second method is slower: it continuously shells out jQuery objects made out of global scope. Try that benchmark again with:
var i=0;
while (targets[i] !== undefined) {
var o = $(targets[i]);
if (needScrollbars(o)) {
wrap(o, id);
id++;
}
i++;
}

Find and execute Javascript fragments in a bunch of HTML

I need to detect and eval the Javascript code contained in a string.
The following code works, but it only evaluates the first <script>...</script> it founds.
function executeJs(html) {
var scriptFragment = "<script(.+?)>(.+?)<\/script>";
match = new RegExp(scriptFragment, "im");
var matches = html.match(match);
if (matches.length >= 2) {
eval(matches[2]);
}
}
I wonder if there is a method that allows me to iterate and execute all Javascript fragments.

The reason it only takes the first one is because you're missing the g flag. Try this:
function executeJs(html) {
var scriptFragment = '<script(.*?)>(.+?)<\/script>';
var re = new RegExp(scriptFragment, 'gim'), match;
while ((match = re.exec(html)) != null) {
eval(match[2]);
}
}
executeJs('<script>alert("hello")</script>abc<script>alert("world")</script>');

Here is some code that does the same thing in a slightly different way. You can pass the string to the function and it will eval all the script tags and return the cleaned source(without script). There is also a slight difference in the way IE handles it, that is handled in the code as well, you may adapt it to your requirements. Also, the evaluated code has the global context. Hope it helps.
function parseScript(_source)
{
var source = _source;
var scripts = new Array();
// Strip out tags
while(source.indexOf("<script") > -1 || source.indexOf("</script") > -1)
{
var s = source.indexOf("<script");
var s_e = source.indexOf(">", s);
var e = source.indexOf("</script", s);
var e_e = source.indexOf(">", e);
// Add to scripts array
scripts.push(source.substring(s_e+1, e));
// Strip from source
source = source.substring(0, s) + source.substring(e_e+1);
}
// Loop through every script collected and eval it
for(var i=0; i<scripts.length; i++)
{
try
{
//eval(scripts[i]);
if(window.execScript)
{
window.execScript(scripts[i]); // IE
}
else
{
window.setTimeout(scripts[i],0); // Changed this from eval() to setTimeout() to get it in Global scope
}
}
catch(ex)
{
// do what you want here when a script fails
alert("Javascript Handler failed interpretation. Even I am wondering why(?)");
}
}
// Return the cleaned source
return source;
}

Blixt should be right...
You may also take a look at prototype's String.evalScripts function.
http://api.prototypejs.org/language/string.html#evalscripts-instance_method