var add = (function () {
var counter = 0;
return function () {
var reset = function() {
counter = 0;
}
return counter += 1;
}
})();
This is a self-invoking function that creates a "private" variable. How would I create a function reset that will reset the counter to 0? I've tried declaring the function inside the closure, but when I call it using add.reset(), it tells me this method is undefined.
You should return the reset function as a method of the object returned by the IIFE. That object needs to be the add function, so put the reset method on it. Just do it like you would in a global context, but inside a closure and return the add function, e.g.:
var add = (function(){
var counter = 0;
function add(n) {
counter += n || 0;
return counter;
}
add.reset = function(){
counter = 0;
return counter;
}
return add;
}())
console.log(add(1)) // 1
console.log(add(4)) // 5
console.log(add.reset()); // 0
However, it would make more sense (to me) to have a counter object that has add and reset methods.
I would recommend that instead of trying to put the function inside your closure, you put your variable outside your closure, like this:
var counter = 0;
var add = function() {
return counter += 1;
};
var reset = function() {
counter = 0;
};
That way the variable has proper scope for what you are trying to accomplish with it.
If you want to explicitly keep the counter declared inside the closure, you need to declare reset (even if you don't give it a value) outside the closure. To use your code, it would look like this:
var reset;
var add = (function () {
var counter = 0;
return function () {
reset = function() {
counter = 0;
}
return counter += 1;
}
})();
Now reset is outside the scope of the add function, so it keeps the value assigned within it!
To be fair, though, there's no reason to assign reset every time you can the result of add... It might be better to do something like:
var reset;
var add = (function () {
var counter = 0;
reset = function() {
counter = 0;
}
return function () {
return counter += 1;
}
})();
Or better still, if you want add.reset() to work:
var counter = function () {
var counter = 0;
this.reset = function() {
counter = 0;
}
this.add = function () {
return counter += 1;
}
};
var add = new counter();
Then add is a full object, which more or less sounds like what you want.
Or if you want to stick with the self invoking function:
var add = (function () {
var counter = 0;
return function () {
this.reset = function() {
counter = 0;
}
return counter += 1;
}
})();
Would probably work. It would be a slightly unusual paradigm from what I've seen though...
If you would like to keep the privacy of your current count, here is an answer that uses an object:
function counter() {
var count = 0;
this.reset = function() {
count = 0;
return count;
};
this.add = function() {
return ++count;
};
}
Then for instance:
var counter1 = new counter();
counter1.add();
console.log(counter1.add());
console.log(counter1.reset());
Related
My code does work but I don't want the jshint errors anymore:
Functions declared within loop referencing an outer scoped variable may lead to confusing semantics
I've tried using let from ES6 to get around the error because I thought that would solve the problem. I configured my gruntfile to use ES6 as well.
I tried using two loops, the outer loop with variable 'i' and the inner loop with variable 'j'
Neither worked.
Full code provided here: https://jsfiddle.net/rwschmitz/zz7ot3uu/
var hobbies = document.getElementsByClassName("hobbies");
var active = false;
// For mouse input
for (var i = 0; i < 5; i++) {
hobbies[i].onmouseover = function() {
hobbies[0].classList.add('hobbies-slide-left');
hobbies[1].classList.add('hobbies-slide-right');
hobbies[2].classList.add('hobbies-slide-left');
hobbies[3].classList.add('hobbies-slide-right');
hobbies[4].classList.add('hobbies-slide-left');
};
}
// For click input
for (var i = 0; i < 5; i++) {
hobbies[i].onclick = function() {
hobbies[0].classList.add('hobbies-slide-left');
hobbies[1].classList.add('hobbies-slide-right');
hobbies[2].classList.add('hobbies-slide-left');
hobbies[3].classList.add('hobbies-slide-right');
hobbies[4].classList.add('hobbies-slide-left');
};
}
You could change your loops to something like this, using Array#forEach():
var hobbies = Array.from(document.getElementsByClassName('hobbies'));
var classes = ['hobbies-slide-left', 'hobbies-slide-right'];
var events = ['mouseover', 'click'];
function addHobbyClass (hobby, index) {
hobby.classList.add(this[index % this.length]);
}
function hobbyEventListener () {
hobbies.forEach(addHobbyClass, classes);
}
hobbies.forEach(function (hobby) {
this.forEach(function (event) {
this.addEventListener(event, hobbyEventListener);
}, hobby);
}, events);
Two additional examples of how to fix the problem.
var hobbies = document.querySelectorAll('.hobbies');
var eventHooks = ['mouseover', 'click'];
hobbies.forEach(function(hobby) {
eventHooks.forEach(function(hook) {
hobby.addEventListener(hook, function() {
hobbies[0].classList.add('hobbies-slide-left');
hobbies[1].classList.add('hobbies-slide-right');
hobbies[2].classList.add('hobbies-slide-left');
hobbies[3].classList.add('hobbies-slide-right');
hobbies[4].classList.add('hobbies-slide-left');
});
});
});
var hobbies = document.getElementsByClassName('hobbies');
var eventHooks = ['mouseover', 'click'];
// Attach events
var attachEvents = function(key) {
eventHooks.forEach(function(hook) {
hobbies[key].addEventListener(hook, function() {
hobbies[0].classList.add('hobbies-slide-left');
hobbies[1].classList.add('hobbies-slide-right');
hobbies[2].classList.add('hobbies-slide-left');
hobbies[3].classList.add('hobbies-slide-right');
hobbies[4].classList.add('hobbies-slide-left');
});
});
};
// Init
var init = function() {
// Loop through hobbies
for (var i = 0; i < hobbies.length; i++) {
attachEvents(i);
}
}
init();
I'm appending onclick events to elements that I'm creating dynamically. I'm using the code below, this is the important part only.
Test.prototype.Show= function (contents) {
for (i = 0; i <= contents.length - 1; i++) {
var menulink = document.createElement('a');
menulink.href = "javascript:;";
menulink.onclick = function () { return that.ClickContent.apply(that, [contents[i]]); };
}
}
First it says that it's undefined. Then I changed and added:
var content = content[i];
menulink.onclick = function () { return that.ClickContent.apply(that, [content]); };
What is happening now is that it always append the last element to all onclick events( aka elements). What I'm doing wrong here?
It's a classical problem. When the callback is called, the loop is finished so the value of i is content.length.
Use this for example :
Test.prototype.Show= function (contents) {
for (var i = 0; i < contents.length; i++) { // no need to have <= and -1
(function(i){ // creates a new variable i
var menulink = document.createElement('a');
menulink.href = "javascript:;";
menulink.onclick = function () { return that.ClickContent.apply(that, [contents[i]]); };
})(i);
}
}
This immediately called function creates a scope for a new variable i, whose value is thus protected.
Better still, separate the code making the handler into a function, both for clarity and to avoid creating and throwing away builder functions unnecessarily:
Test.prototype.Show = function (contents) {
for (var i = 0; i <= contents.length - 1; i++) {
var menulink = document.createElement('a');
menulink.href = "javascript:;";
menulink.onclick = makeHandler(i);
}
function makeHandler(index) {
return function () {
return that.ClickContent.apply(that, [contents[index]]);
};
}
};
A way to avoid this problem altogether, if you don't need compatibility with IE8, is to introduce a scope with forEach, instead of using a for loop:
Test.prototype.Show = function (contents) {
contents.forEach(function(content) {
var menulink = document.createElement('a');
menulink.href = "javascript:;";
menulink.onclick = function() {
return that.ClickContent.call(that, content);
};
});
}
I'm writing a counter to count an object, and it looks like this:
function myFunc(param) {
this.param = param;
param.foo = function() {
var object = window.JSON.parse(data);
for (i in object) {
counter++;
}
}
}
var foo = new myFunc('data.json');
var counter = 0;
document.write(counter); // displays 0
How can I achieve to get the counter value outside the function? I tried almost everything, from window to return to separate functions.
Any clue?
Update
I prefer a better design like this
function myFunc(param) {
this.param = param;
param.foo = function() {
var object = window.JSON.parse(data);
var counter = 0;
for (i in object) {
counter++;
}
return counter;
}
}
var foo = new myFunc('data.json');
document.write(counter); // displays undefined
Update 2
Sorry, thought it would be easier to have a sample code. But here's the real one: https://gist.github.com/BobWassermann/e709ec303477a015b609
I think you have a couple issues here.
First, you're setting your counter to 0 just before you write. It will always be 0 no matter what you do, even with hoisting.
Second, you never call the foo function, so your counter is never incremented.
Third, param.foo isn't public. I think you want it to be this.foo = function(){ ... }.
Here's a simplified version of the code you posted with my tweaks:
var counter = 0;
var foo;
function myFunc() {
this.foo = function() {
counter = 1000;
}
}
foo = new myFunc();
foo.foo();
document.write(counter);
JSFiddle: http://jsfiddle.net/dgrundel/2ojw2332/2/
Note that JSFiddle doesn't allow document.write, so replaced that part.
function myFunc(param) {
this.param = param;
this.foo = function () {
var object = window.JSON.parse(this.param),
counter = 0,
i;
for (i in object) {
counter++;
}
return counter;
};
}
var foo = new myFunc('{"a":99}');
out(foo.foo());
function out(s) {
document.getElementById('out').innerHTML = '<pre>' + s + '</pre>';
}
<div id="out"></div>
As #Nina Scholz pointed out earlier, I'm retrieving the data asynchron. Javascript started painting the dom before all the values where loaded.
This fixed my problem:
if (document.readyState) {
setTimeout(function() {
var objLen = Object.keys(obj).length;
console.log(objLen);
}, 100);
}
I'm waiting for the document to be ready, then add an additional timeout as buffer.
var t = 0;
function addDiv()
{
var div = document.createElement("div");
t++;
div.setAttribute("id", "box" + t);
document.body.appendChild(div);
AddStyle();
}
var h = 0;
var p = 1;
function doMove()
{
var okj = document.getElementById("box" + p);
if (p <= t) {
p++;
}
var g = setInterval(function () {
var go = parseInt(okj.style.left, 0) + 1 + "px";
okj.style.left = go;
}, 1000 / 60);
}
My question is that after the p increments that is p++ will my var p = 1 be incremented everytime I call doMove? Please help me regarding this matter.
By definition global variables have global scope, so you can increment them or re-assign them within a function and that will work, how fantastic is that!
Although as Borgtex has pointed out your if statement won't work
if (p <= t) {
p++;
}
You have declared the variable t in another function so your doMove() function does not have access to it, therefore this statement will always return false; If you make t a global variable or pass it into your doMove() function as a parameter then this will work.
var p = 1; // this variable is global
function varTest(){
p++ //This will work because p is global so this function has access to it.
var t = 0;
}
function anotherTest(){
if(p<t){ //This will return false - t is not in scope as it was defined in another function
alert("supercalifragilisticexpihalitoscious");
}
}
I am using anonymous function assigned to a variable to minimize use of global variables. Within this function there are nested functions: one to preload and resize images, and two other nested functions for navigation (next and previous). The code below generates error that the variable to which the anonymous function is assigned is not defined:
Cannot read property 'preload_and_resize' of undefined
If you spot the problem please let me know. Thank you very much.
<html>
<head>
<script type="text/javascript">
var runThisCode=(function(){
var myImages=new Array("img/01.jpg","img/02.jpg","img/03.jpg");
var imageObj = new Array();
var index=0;
var preload_and_resize=function(){
var i = 0;
var imageArray = new Array();
for(i=0; i<myImages.length; i++) {
imageObj[i] = new Image();
imageObj[i].src=myImages[i];
}
document.pic.style.height=(document.body.clientHeight)*0.95;
};
var next_image=function(){
index++;
if(index<imageObj.length){
document.pic.src=imageObj[index].src;
}
else{
index=0;
document.pic.src=imageObj[index].src;
}
};
var prev_image=function(){
index--;
if(index>=0){
document.pic.src=imageObj[index].src;
}
else{
index=myImages.length-1;
document.pic.src=imageObj[index].src;
}
};
})();
</script>
</head>
<body onload="runThisCode.preload_and_resize();">
<div align="center">
<img name="pic" id="pic" src="img/01.jpg"><br />
PrevNext
</div>
</body>
</html>
Your anonymous function doesn't return anything, so when you run it, undefined gets returned. That's why runThisCode is undefined. Regardless though, with the way you've written it, preload_and_resize will be local, so you wouldn't be able to access that anyway.
Instead, you want this anonymous function to construct an object, and reutrn that. Something like this should work, or at least get you close:
var runThisCode=(function(){
var result = {};
result.myImages=new Array("img/01.jpg","img/02.jpg","img/03.jpg");
result.imageObj = new Array();
result.index=0;
result.preload_and_resize=function(){
var i = 0;
var imageArray = new Array();
for(i=0; i< result.myImages.length; i++) {
imageObj[i] = new Image();
imageObj[i].src=myImages[i];
}
document.pic.style.height=(document.body.clientHeight)*0.95;
};
result.next_image=function(){
index++;
if(index<imageObj.length){
document.pic.src=imageObj[index].src;
}
else{
index=0;
document.pic.src=imageObj[index].src;
}
};
result.prev_image=function(){
index--;
if(index>=0){
document.pic.src=imageObj[index].src;
}
else{
index=myImages.length-1;
document.pic.src=imageObj[index].src;
}
};
return result;
})();
This should explain what you are doing wrong :
var foobar = (function (){
var priv1, priv2 = 'sum' , etc;
return {
pub_function: function() {},
another: function() {
console.log('cogito ergo ' + priv2 );
}
};
})();
foobar.another();
You've assigned the function to the variable next_image which is scoped to the self-invoking anonymous function.
The value you assign to runThisCode is the return value of that anonymous function, which (since there is no return statement) is undefined.
To get the code to work you need to assign an object to runThisCode and make next_image a member of it.
Add the following to the end of the anonymous function:
return {
"next_image": next_image
}
Remove the anonymous function, and make your function public. You will only create one global variable: the object runThisCode.
var runThisCode = function () {
var myImages = new Array("img/01.jpg", "img/02.jpg", "img/03.jpg");
var imageObj = new Array();
var index = 0;
this.preload_and_resize = function () {
var i = 0;
var imageArray = new Array();
for (i = 0; i < myImages.length; i++) {
imageObj[i] = new Image();
imageObj[i].src = myImages[i];
}
document.pic.style.height = (document.body.clientHeight) * 0.95;
};
this.next_image = function () {
index++;
if (index < imageObj.length) {
document.pic.src = imageObj[index].src;
} else {
index = 0;
document.pic.src = imageObj[index].src;
}
};
this.prev_image = function () {
index--;
if (index >= 0) {
document.pic.src = imageObj[index].src;
} else {
index = myImages.length - 1;
document.pic.src = imageObj[index].src;
}
};
};
And then, later in your code:
runThisCode.preload_and_resize();
should work.
From the invocation you've got in body onload property, it looks like what you're trying to achieve with the IIFE (immediately invoked function expression) is return an object that has a the method preload_and_resize.
As others have pointed out, you're not returning anything from the IIFE, so really all that's happening is you're closing up everything inside it in its own namespace, but not "exporting" anything.
If you want to "export" those functions, from your IIFE, you'd probably add a final bit to it that looked something like this:
return {
'preload_and_resize': preload_and_resize,
'next_image': next_image,
'prev_image': prev_image
}
which essentially creates a new JavaScript object literal, and then assigns its properties to the function values from the local scope.
Some developers would find this redundant and rather than finishing out with this sort of explicit export would probably just define the functions while declaring the object literal, something like:
return {
preload_and_resize: function(){
var i = 0;
var imageArray = new Array();
for(i=0; i<myImages.length; i++) {
imageObj[i] = new Image();
imageObj[i].src=myImages[i];
}
document.pic.style.height=(document.body.clientHeight)*0.95;
},
next_image: function() {
index++;
if(index<imageObj.length){
document.pic.src=imageObj[index].src;
}
else {
index=0;
document.pic.src=imageObj[index].src;
}
},
prev_image: function() {
index--;
if(index>=0){
document.pic.src=imageObj[index].src;
}
else {
index=myImages.length-1;
document.pic.src=imageObj[index].src;
}
}
}
In respect of previous answers, my version:
function(self) {
let myImages = new Array("img/01.jpg", "img/02.jpg", "img/03.jpg");
let imageObj = new Array();
let index = 0; // if you need to expose this call with self.index
self.preload_and_resize = function() {
let i = 0;
let imageArray = new Array();
let (i = 0; i < myImages.length; i++) {
imageObj[i] = new Image();
imageObj[i].src = myImages[i];
}
document.pic.style.height = (document.body.clientHeight) * 0.95;
};
var next_image = function() {
index++;
if (index < imageObj.length) {
document.pic.src = imageObj[index].src;
} else {
index = 0;
document.pic.src = imageObj[index].src;
}
};
var prev_image = function() {
index--;
if (index >= 0) {
document.pic.src = imageObj[index].src;
} else {
index = myImages.length - 1;
document.pic.src = imageObj[index].src;
}
};
})(window.myCurrentPage = window.myCurrentPage || {});
// now you canll myCurrentPage.preload_and_resize();