I am very new to javascript.
Here I am failing to run an object method on a DOM element that I selected through another property of the same object. I suspect there is something wrong with my thinking!
Thanks in advance for any piece of help.
var Arrow = function() {
this.current = $('.arrow');
this.previous = null;
this.bend = function() {
// do bend
};
};
var arrow = new Arrow();
arrow.current.bend();
bend() is a method of Arrow, not current. Use arrow.bend() and it will also have access to current using this.current.
arrow.current.bend is not defined.
You have defined:
this.current as the Array of DOM elements.
this.bend as method with a function.
Hence, you can call:
arrow.current >> returns Array of DOMs
arrow.bend() >> executes function bend.
arrow.current.bend() does not exist.
Also, note that arrow.current is an array. You'd first need to get each of the elements:
for (element of arrow.current) { element.bend(); }
However, as said before, element does not have a bend element by default and you have not appended at any point. Only arrow has a bend property.
I hope this guides you on why this does not work.
However, if you want to open a question on what you are trying to achieve, maybe we can help to get it fixed.
You need to call bend() on arrow object. In bend() function, you do what you need to do.
var Arrow = function() {
this.current = $('.arrow');
this.previous = null;
this.bend = function() {
// do bend
current.style = 'bent';
};
};
var arrow = new Arrow();
arrow.bend();
So two things.
You called the right method on the wrong object
arrow.bend(); // not arrow.current.bend()
The second possible problem is with this.current = $('.arrow');. To get the an element from the DOM, you should make sure it's totally loaded. I'd suggest the following
var Arrow = function($arrow) {
this.current = $arrow;
this.previous = null;
};
// To avoid creating the `bend` in every instance of Arrow
Arrow.prototype.bend = function() {
console.log(this.current.attr('id'));
};
$(function () {
// Now it's certain that the DOM is completely loaded
var arrow = new Arrow($('.arrow').first());
arrow.bend();
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div class="arrow" id="toto">arrow<div>
Related
In the code below, I'm looping through each "player_visualizer" element and attempting to create a new P5 instance for each element.
If I console.log(context) in the loop I will get the context of that particular element, which is exactly what I need.
$('.player_visualizer').each(function (i) {
context = $(this);
playerVisualizersP5[i] = new p5(playerVisualizer, context);
});
However, The trouble I'm having is passing the context of that particular element to the function that will handle all of the P5 animations.
For example, when I try and pass that context variable to the function below and do console.log(p.context), the context variable is always undefined.
let playerVisualizer = function (p, context) {
p.context = context;
}
I've done a fair amount of research on what I could do about this, but I can't seem to tie it back to my particular situation. I've narrowed down my research to a few resources below.
http://hugoware.net/blog/passing-context-with-javascript
How do I pass the this context to a function?
Any help or guidance is greatly appreciated.
Why do you believe that passing something into the p5 constructor will automatically pass that argument into the playerVisualizer function?
From the P5.js documentation:
One final note: when creating a p5 instance, you can specify a second
argument (HTML element id) which acts the parent for all elements
created by the sketch. For example, let's say you have:
<body>
<div id = "p5sketch">
</div>
<p>Some other HTML</p>
</body>
You can now say:
var myp5 = new p5(s,'p5sketch');
And all elements will be created inside that div.
This means the only valid second argument is a string ID, which gets used by P5.js but isn't passed into the sketch function.
To understand better what's going on, let's look at this example:
var s = function( sketch ) {
sketch.setup = function() {
sketch.createCanvas(200, 200);
};
sketch.draw = function() {
sketch.background(128);
};
};
var myp5 = new p5(s);
In this example sketch, there are a few things to understand:
myp5 is an instance of p5, which contains P5.js functions like setup() and draw() and background().
s is a sketch function, which takes an instance of p5.
sketch is an instance of p5, which s can use to access P5.js functions.
In other words, myp5 and sketch are the same object.
This is useful to you, because if you want to pass data into sketch, you can pass that data into myp5, like this:
var s = function( sketch ) {
sketch.setup = function() {
sketch.createCanvas(200, 200);
};
sketch.draw = function() {
sketch.background(128);
sketch.text(sketch.extraThing, 20, 20);
};
};
var myp5 = new p5(s);
myp5.extraThing = "testing";
I am very new to programming and I am wondering if anyone can help me with this.
I am trying to make a pop up page.
I set variables for each click area which I set each area with div and placed with css.
Also for each pop up image which I put div id on each image on html and set display = "none" on css.
I want to make a function that shows one image on touchend and hide other images at the same time.
Could you help me with my code?
var pop = new Array("pop1","pop2","pop3","pop4","pop5","pop6");
var clickArea = new Array("click1","click2","click3","click4","click5","click6");
function diplay(click,show,hide){
click.addEventListner("touchend",function(){
show.style.display = "block";
hide.style.display = "none";
});
};
display("click[0]","pop[0]","pop[1,2,3,4,5]");
There are a few different issues with your code.
You used strings instead of the actual code structure references while calling display. I see that you mean for these to reference the element ids, but you must first get the element with document.getElementById(...) or jQuery's $("#...").
In the pop and clickArea arrays, you used strings, which do not have the .style object. You need to reference the elements themselves.
Your code structure is not designed to handle arrays.
You need to define the addEventListener before you need the function handler to be called. You do not want this every time.
The click argument in the display function is redundant, as it is never called.
You are using jQuery. You should have stated this! (but you're forgiven) :)
You can't reach into arrays with the syntax arrayName[#,#,#].
You misspelled "display". Whoops!
The arrays are redundant, since the code needed to be restructured.
First, in order to address Point #4, we need this code to run when the DOM has finished loading:
var clickArea = new Array("click1","click2","click3","click4","click5","click6");
clickArea.each(function(id){
$("#"+id)[0].addEventListener("touchend", display);
});
Next, we need to fix the issues with your code. They're explained above.
var pop = new Array("pop1","pop2","pop3","pop4","pop5","pop6");
function display(event){
var indx = Number(event.target.id.split(/\D/i).join(""));
$("#pop"+indx)[0].style.display = "block";
pop.each(function(ide) {
if (ide.split(/\D/i).join("") != indx-1) {
$("#"+ide)[0].style.display = "none";
}
});
};
Otherwise, great job! All of us started out like this, and believe in you! Keep it up!
P.S. You can set arrays like this [ ? , ? , ? , ? ] instead of this new Array( ? , ? , ? , ? ).
Here is an example using for loops instead of methods of Arrays etc
Start off by defining everything you can
var popup_id = ["pop1", "pop2", "pop3", "pop4", "pop5", "pop6"],
popup_elm = [], // for referencing the elements later
area_id = ["click1", "click2", "click3", "click4", "click5", "click6"],
area_elm = [], // for referencing the elements later
i; // for the for -- don't forget to var everything you use
// a function to hide all popups
function hideAll() {
var i; // it's own var means it doesn't change anything outside the function
for (i = 0; i < popup_elm.length; ++i) {
popup_elm.style.display = 'none';
}
}
// a function to attach listeners
function listenTouch(area, popup) {
area.addEventListener('touchend', function () {
hideAll();
popup.style.display = 'block';
});
// we did this in it's own function to give us a "closure"
}
Finally we are ready do begin linking it all to the DOM, I'm assuming the following code is executed after the elements exist in the browser
// setup - get Elements from ids, attach listeners
for (i = 0; i < popup_id.length; ++i) {
popup_elm[i] = document.getElementById(popup_id[i]);
area_elm[i] = document.getElementById(area_id[i]);
listenTouch(area_elm[i], popup_elm[i]);
}
You cannot treat strings as html elements.
Assuming there are elements with click area ids in the page, you may do something like (once the document is ready).
var popEls = pop.map(function (id) { return document.getElementById(id) });
clickArea.forEach(function (id) {
var clickAreaEl = document.getElementById(id);
clickAreaEl.addEventListener('click', onClickAreaClick);
});
function onClickAreaClick() {
var clickAreaNum = +this.id.match(/\d+$/)[0],
popIndex = clickAreaNum - 1;
popEls.forEach(function (popEl) {
popEl.style.display = 'none';
});
popEls[popIndex].style.display = 'block';
}
Let's say I have a setup like this.
var Account = function(data) {
this.data = data;
this.domElement = (function(){ code that generates DOM element that will represent this account })();
this.domElement.objectReference = this;
}
Account.prototype = {
show: function() { this.domElement.classList.remove('hidden'); },
hide: function() { this.domElement.classList.add('hidden') }
}
My question is about the last line: this.domElement.objectReference = this;
It would be a useful thing to have because then I can add event listeners to my DOM element and still get access to the object itself. I can add methods that would affect my DOM element, such as hide() and show(), for instance, without having to resort to modifying visibility of the DOM element using CSS directly.
I tested this code and it works like I want it to, but I'm curious whether this would cause memory leaks or some other unpleasantness or if it's an acceptable thing to do?
Thank you!
Luka
I know this has been answered by #PaulS. already, but I find the answer counter intuitive (returning a DOM element from the Account constructor is not expected) and too DOM-centric, but at the same time the implementation is very simple, so I am not sure what to think ;)
Anyway, I just wanted to show a different way of doing it. You can store Account instances in a map and give them a unique id (perhaps they have one already), then you store that id as a data attribute on the DOM element. Finally you implement a getById function or something similar to retrieve the account instance by id from the listeners.
That's pretty much how jQuery's data works.
Here's an example with delegated events like you wanted from the comments.
DEMO
var Account = (function (accounts, id) {
function Account(data) {
accounts[this._id = ++id] = this;
this.el = createEl.call(this);
}
Account.prototype = {
constructor: Account,
show: function() { this.el.classList.remove('hidden'); },
hide: function() { this.el.classList.add('hidden'); }
};
function createEl() {
var el = this.el = document.createElement('div');
el.className = 'account';
el.innerHTML = el.dataset.accountId = this._id;
return el;
}
Account.getById = function (id) {
return accounts[id];
};
Account.init = function () {
//add delegate listeners
document.addEventListener('click', function (e) {
var target = e.target,
account = Account.getById(target.dataset.accountId);
if (!account) return;
account.hide();
});
};
return Account;
})({}, 0);
//once DOM loaded
Account.init(); //start listening to events
var body = document.body;
body.appendChild(new Account().el);
body.appendChild(new Account().el);
Why not have domElement as a variable, and return it from your function? To keep the reference to your constructed Object (but only where this is as expected), you could do a if (this instanceof Account) domElement.objectReference = this;
You've now saved yourself from circular references and can access both the Node and the Object. Doing it this way around is more helpful if you're expecting to lose the direct reference to your Account instance, but expect to need it when "looking up" the Node it relates to at some later time.
Code as requested
var Account = function (data) {
var domElement; // var it
this.data = data;
domElement = (function(){/* ... */}()); // use var
if (this instanceof Account)
domElement.objectReference = this; // assign `this`
return domElement;
};
// prototype as before
Returned element is now the Node, not the Object; so you'd access the Account instance like this
var domElement = new Account();
domElement.objectReference.show(); // for example
In my opinion there is nothing good about referencing the object inside of the object itself. The main reason for this is complexity and obscurity.
If you would point out how exactly are you using this domElement.objectReference later in the code, I am sure that I or someone else would be able to provide a solution without this reference.
I have an object which creates a slideshow.
I want to have several slideshows on a page
I have an event handler for slideshow element inside it
I want the event handler to know which slideshow object has created an item clicked
-
slideshow=function(){
var g = document.createElement(...);
...
g.onclick = f1;
f1 = function(slideshow_instance, event) {
//EXPLAIN ME HOW TO GET THE slideshow_instance
}
}
var sl1 = new slideshow();
var sl2 = new slideshow();
Clicking on an element slideshow has created should return either
sl1
or
sl2
I explain well?
Short answer, use: this.
Longer answer, what you want is:
slideshow=function(){
/* ... */
var self = this;
f1 = function(event) {
// do stuff with self.
}
}
The reason you need to point to this using self is that event handlers will change the meaning of this when they are called. But at the time the object is created this properly refer to the correct object (an instance of slideshow). The reason we can access the self variable during event callback is because it has been captured by a closure.
Feel free to google or search on stackoverflow any word/terminology from the above description if you need further explanation.
slideshow=function(){
var g = document.createElement(...);
g._objRef = this;
...
g.onclick = f1;
f1 = function(event) {
alert(this._objRef);
}
}
var sl1 = new slideshow();
var sl2 = new slideshow();
A bit of a hack imo, but it should do the trick.
I edited the question so it would make more sense.
I have a function that needs a couple arguments - let's call it fc(). I am passing that function as an argument through other functions (lets call them fa() and fb()). Each of the functions that fc() passes through add an argument to fc(). How do I pass fc() to each function without having to pass fc()'s arguments separately? Below is how I want it to work.
function fa(fc){
fc.myvar=something
fb(fc)
}
function fb(fc){
fc.myothervar=something
fc()
}
function fc(){
doessomething with myvar and myothervar
}
Below is how I do it now. As I add arguments, it's getting confusing because I have to add them to preceding function(s) as well. fb() and fc() get used elsewhere and I am loosing some flexibility.
function fa(fc){
myvar=something
fb(fc,myvar)
}
function fb(fc,myvar){
myothervar=something
fc(myvar,myothervar)
}
function fc(myvar,myothervar){
doessomething with myvar and myothervar
}
Thanks for your help
Edit 3 - The code
I updated my code using JimmyP's solution. I'd be interested in Jason Bunting's non-hack solution. Remember that each of these functions are also called from other functions and events.
From the HTML page
<input type="text" class="right" dynamicSelect="../selectLists/otherchargetype.aspx,null,calcSalesTax"/>
Set event handlers when section is loaded
function setDynamicSelectElements(oSet) {
/**************************************************************************************
* Sets the event handlers for inputs with dynamic selects
**************************************************************************************/
if (oSet.dynamicSelect) {
var ySelectArgs = oSet.dynamicSelect.split(',');
with (oSet) {
onkeyup = function() { findListItem(this); };
onclick = function() { selectList(ySelectArgs[0], ySelectArgs[1], ySelectArgs[2]) }
}
}
}
onclick event builds list
function selectList(sListName, sQuery, fnFollowing) {
/**************************************************************************************
* Build a dynamic select list and set each of the events for the table elements
**************************************************************************************/
if (fnFollowing) {
fnFollowing = eval(fnFollowing)//sent text function name, eval to a function
configureSelectList.clickEvent = fnFollowing
}
var oDiv = setDiv(sListName, sQuery, 'dynamicSelect', configureSelectList); //create the div in the right place
var oSelected = event.srcElement;
if (oSelected.value) findListItem(oSelected)//highlight the selected item
}
Create the list
function setDiv(sPageName, sQuery, sClassName, fnBeforeAppend) {
/**************************************************************************************
* Creates a div and places a page in it.
**************************************************************************************/
var oSelected = event.srcElement;
var sCursor = oSelected.style.cursor; //remember this for later
var coords = getElementCoords(oSelected);
var iBorder = makeNumeric(getStyle(oSelected, 'border-width'))
var oParent = oSelected.parentNode
if (!oParent.id) oParent.id = sAutoGenIdPrefix + randomNumber()//create an ID
var oDiv = document.getElementById(oParent.id + sWindowIdSuffix)//see if the div already exists
if (!oDiv) {//if not create it and set an id we can use to find it later
oDiv = document.createElement('DIV')
oDiv.id = oParent.id + sWindowIdSuffix//give the child an id so we can reference it later
oSelected.style.cursor = 'wait'//until the thing is loaded
oDiv.className = sClassName
oDiv.style.pixelLeft = coords.x + (iBorder * 2)
oDiv.style.pixelTop = (coords.y + coords.h + (iBorder * 2))
XmlHttpPage(sPageName, oDiv, sQuery)
if (fnBeforeAppend) {
fnBeforeAppend(oDiv)
}
oParent.appendChild(oDiv)
oSelected.style.cursor = ''//until the thing is loaded//once it's loaded, set the cursor back
oDiv.style.cursor = ''
}
return oDiv;
}
Position and size the list
function configureSelectList(oDiv, fnOnClick) {
/**************************************************************************************
* Build a dynamic select list and set each of the events for the table elements
* Created in one place and moved to another so that sizing based on the cell width can
* occur without being affected by stylesheet cascades
**************************************************************************************/
if(!fnOnClick) fnOnClick=configureSelectList.clickEvent
if (!oDiv) oDiv = configureSelectList.Container;
var oTable = getDecendant('TABLE', oDiv)
document.getElementsByTagName('TABLE')[0].rows[0].cells[0].appendChild(oDiv)//append to the doc so we are style free, then move it later
if (oTable) {
for (iRow = 0; iRow < oTable.rows.length; iRow++) {
var oRow = oTable.rows[iRow]
oRow.onmouseover = function() { highlightSelection(this) };
oRow.onmouseout = function() { highlightSelection(this) };
oRow.style.cursor = 'hand';
oRow.onclick = function() { closeSelectList(0); fnOnClick ? fnOnClick() : null };
oRow.cells[0].style.whiteSpace = 'nowrap'
}
} else {
//show some kind of error
}
oDiv.style.width = (oTable.offsetWidth + 20) + "px"; //no horiz scroll bars please
oTable.mouseout = function() { closeSelectList(500) };
if (oDiv.firstChild.offsetHeight < oDiv.offsetHeight) oDiv.style.height = oDiv.firstChild.offsetHeight//make sure the list is not too big for a few of items
}
Okay, so - where to start? :) Here is the partial function to begin with, you will need this (now and in the future, if you spend a lot of time hacking JavaScript):
function partial(func /*, 0..n args */) {
var args = Array.prototype.slice.call(arguments, 1);
return function() {
var allArguments = args.concat(Array.prototype.slice.call(arguments));
return func.apply(this, allArguments);
};
}
I see a lot of things about your code that make me cringe, but since I don't have time to really critique it, and you didn't ask for it, I will suggest the following if you want to rid yourself of the hack you are currently using, and a few other things:
The setDynamicSelectElements() function
In this function, you can change this line:
onclick = function() { selectList(ySelectArgs[0], ySelectArgs[1], ySelectArgs[2]) }
To this:
onclick = function() { selectList.apply(null, ySelectArgs); }
The selectList() function
In this function, you can get rid of this code where you are using eval - don't ever use eval unless you have a good reason to do so, it is very risky (go read up on it):
if (fnFollowing) {
fnFollowing = eval(fnFollowing)
configureSelectList.clickEvent = fnFollowing
}
And use this instead:
if(fnFollowing) {
fnFollowing = window[fnFollowing]; //this will find the function in the global scope
}
Then, change this line:
var oDiv = setDiv(sListName, sQuery, 'dynamicSelect', configureSelectList);
To this:
var oDiv = setDiv(sListName, sQuery, 'dynamicSelect', partial(configureSelectListAlternate, fnFollowing));
Now, in that code I provided, I have "configureSelectListAlternate" - that is a function that is the same as "configureSelectList" but has the parameters in the reverse order - if you can reverse the order of the parameters to "configureSelectList" instead, do that, otherwise here is my version:
function configureSelectListAlternate(fnOnClick, oDiv) {
configureSelectList(oDiv, fnOnClick);
}
The configureSelectList() function
In this function, you can eliminate this line:
if(!fnOnClick) fnOnClick=configureSelectList.clickEvent
That isn't needed any longer. Now, I see something I don't understand:
if (!oDiv) oDiv = configureSelectList.Container;
I didn't see you hook that Container property on in any of the other code. Unless you need this line, you should be able to get rid of it.
The setDiv() function can stay the same.
Not too exciting, but you get the idea - your code really could use some cleanup - are you avoiding the use of a library like jQuery or MochiKit for a good reason? It would make your life a lot easier...
A function's properties are not available as variables in the local scope. You must access them as properties. So, within 'fc' you could access 'myvar' in one of two ways:
// #1
arguments.callee.myvar;
// #2
fc.myvar;
Either's fine...
Try inheritance - by passing your whatever object as an argument, you gain access to whatever variables inside, like:
function Obj (iString) { // Base object
this.string = iString;
}
var myObj = new Obj ("text");
function InheritedObj (objInstance) { // Object with Obj vars
this.subObj = objInstance;
}
var myInheritedObj = new InheritedObj (myObj);
var myVar = myInheritedObj.subObj.string;
document.write (myVar);
subObj will take the form of myObj, so you can access the variables inside.
Maybe you are looking for Partial Function Application, or possibly currying?
Here is a quote from a blog post on the difference:
Where partial application takes a function and from it builds a function which takes fewer arguments, currying builds functions which take multiple arguments by composition of functions which each take a single argument.
If possible, it would help us help you if you could simplify your example and/or provide actual JS code instead of pseudocode.