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JavaScript closure inside loops – simple practical example
(44 answers)
Closed 8 years ago.
var smartActionsId = ['smartActions1','smartActions5','smartActions10'];
for (var i in smartActionsId) {
console.log("smartActionsId ="+smartActionsId[i]);
$('#' + smartActionsId[i] + ' select').change(function () {
var value = $(this).val();
var disableValue;
var ruleIndex = smartActionsId[i].substr(11);
console.log("smartActionsId ="+smartActionsId[i]+" i ="+i);
if (value === '0') {
disableValue = true;
onRuleToggle(disableValue, ruleIndex)
}
else if (value === '1') {
disableValue = false;
onRuleToggle(disableValue, ruleIndex)
}
});
}
I'm creating change event dynamically for a multiple switch slider items using the above JavaScript code. But problem I'm facing is, when I click on any switch 'i' value gets replaced with the last value i.e. in smartActionsId I have 3 elements, which ever switch I change it effects for last switch (smartActions10).
Could you please help me resolving this issue?
Other answers here fixed your problem, but I think you can refactor your code a little and make it much more understandable.
First, I don't like IDs. in your scenario, you have multiple ids which needs to be treated the same. Why not use one mighty class?
Also, ruleIndex calculated from element's ID? smells rotten.
If it tells you something about the element, it should be in an attribute or a data-* attribute.
The first bit of code fixes the markup by adding ruleIndex as data attribute and adding a .smart-actionable class. (Maybe you can even move this part to the server-side, to provide yourself with easier markup for JS).
Now, this makes the event handling quite simple.
var smartActionsId = ['smartActions1','smartActions5','smartActions10'];
for (var i in smartActionsId) {
$('#' + smartActionsId[i])
.data('ruleIndex', smartActionsId[i].substr(11))
.addClass('smart-actionable');
}
$('.smart-actionable').on('change', 'select', function() {
var value = $(this).val();
var disableValue = (value === '0');
onRuleToggle(disableValue, $(this).data('ruleIndex'));
});
Hope it will help.
You don't want to attach event listeners inside a for loop because the variable that tracks the index is used by each loop cycle. If you do that, the i variable will always equal the length of the array minus 1. Use Array.prototype.forEach() instead to prevent that.
var smartActionsId = ['smartActions1','smartActions5','smartActions10'];
smartActionsId.forEach(function (identifier, index) {
console.log("smartActionsId ="+identifier);
$('#' + smartActionsId[index] + ' select').change(function () {
var value = $(this).val();
var disableValue;
var ruleIndex = smartActionsId[index].substr(11);
console.log("smartActionsId ="+smartActionsId[index]+" index ="+index);
if (value === '0') {
disableValue = true;
onRuleToggle(disableValue, ruleIndex)
}
else if (value === '1') {
disableValue = false;
onRuleToggle(disableValue, ruleIndex)
}
});
});
Please Note: IE8 and down does NOT support Array.prototype.forEach().
You cant use for...in in this case. Please try the code below:
var smartActionsId = ['smartActions1', 'smartActions5', 'smartActions10'];
for (var i = 0; i < smartActionsId.length; i++) {
console.log("smartActionsId =" + smartActionsId[i]);
$('#' + smartActionsId[i] + ' select').change(function() {
var value = $(this).val();
var disableValue;
var ruleIndex = smartActionsId[i].substr(11);
console.log("smartActionsId =" + smartActionsId[i] + " i =" + i);
if (value === '0') {
disableValue = true;
onRuleToggle(disableValue, ruleIndex)
} else if (value === '1') {
disableValue = false;
onRuleToggle(disableValue, ruleIndex)
}
});
}
I've always use names like smartActions_1. If you can use it, then in your .change function you can use
// if 'smartActionsId' is global variable
// and if you need to get position in 'smartActionsId' array
var numInArray = $.inArray( this.parentNode.id, smartActionsId );
// this - your select DOM object
var ruleIndex = parseInt( this.parentNode.id.split( "_" )[ 1 ] );
And remember that this in .change function its select which have no id and you must use this.parentNode or $( this ).parent() to get it's holder (I think its div or somethink like that).
#Jack in comments is right: select may not be a direct child. Then you can use this code:
var parent = $( this ).closest( "[id^=smartActions]" );
var numInArray = $.inArray( parent.attr( "id" ), smartActionsId );
var ruleIndex = parseInt( parent.attr( "id" ).split( "_" )[ 1 ] );
I have a plugin that is cloning an input that may or may not have the jQuery validation engine bound to it.
so, it's classes may contain e.g. validate[required,custom[number],min[0.00],max[99999.99]] or any combination of the jQuery validation engine validators.
The only for sure thing is that the class begins with validate[ and ends with ], but to make it more complicated as in the example above, there can be nested sets of [].
So, my question is, how can I remove these classes (without knowing the full class) using jQuery?
Here is my implementation, It's not using regex, but meh, who said it had too?
//'first validate[ required, custom[number], min[0.00], max[99999.99] ] other another';
var testString = $('#test')[0].className;
function removeValidateClasses(classNames) {
var startPosition = classNames.indexOf("validate["),
openCount = 0,
closeCount = 0,
endPosition = 0;
if (startPosition === -1) {
return;
}
var stringStart = classNames.substring(0, startPosition),
remainingString = classNames.substring(startPosition),
remainingSplit = remainingString.split('');
for (var i = 0; i < remainingString.length; i++) {
endPosition++;
if (remainingString[i] === '[') {
openCount++;
} else if (remainingString[i] === ']') {
closeCount++;
if (openCount === closeCount) {
break;
}
}
}
//concat the strings, without the validation part
//replace any multi-spaces with a single space
//trim any start and end spaces
return (stringStart + remainingString.substring(endPosition))
.replace(/\s\s+/g, ' ')
.replace(/^\s+|\s+$/g, '');
}
$('#test')[0].className = removeValidateClasses(testString);
It might actually be simpler to do that without JQuery. Using the className attribute, you can then get the list of classes using split(), and check whether the class contains "validate[".
var classes = $('#test')[0].className.split(' ');
var newClasses = "";
for(var i = 0; i < classes.length; i++){
if(classes[i].indexOf('validate[') === -1){
newClasses += classes[i];
}
}
$('#test')[0].className = newClasses
I think this solution is even more simple. You just have to replace field_id with the id of that element and if the element has classes like some_class different_class validate[...] it will only remove the class with validate, leaving the others behind.
var that ='#"+field_id+"';
var classes = $(that).attr('class').split(' ');
$.each(classes, function(index, thisClass){
if (thisClass.indexOf('validate') !== -1) {
$(that).removeClass(classes[index])
}
});
Using plain JavaScript (not jQuery), Is there any way to check if an element contains a class?
Currently, I'm doing this:
var test = document.getElementById("test");
var testClass = test.className;
switch (testClass) {
case "class1":
test.innerHTML = "I have class1";
break;
case "class2":
test.innerHTML = "I have class2";
break;
case "class3":
test.innerHTML = "I have class3";
break;
case "class4":
test.innerHTML = "I have class4";
break;
default:
test.innerHTML = "";
}
<div id="test" class="class1"></div>
The issue is that if I change the HTML to this...
<div id="test" class="class1 class5"></div>
...there's no longer an exact match, so I get the default output of nothing (""). But I still want the output to be I have class1 because the <div> still contains the .class1 class.
Use element.classList .contains method:
element.classList.contains(class);
This works on all current browsers and there are polyfills to support older browsers too.
Alternatively, if you work with older browsers and don't want to use polyfills to fix them, using indexOf is correct, but you have to tweak it a little:
function hasClass(element, className) {
return (' ' + element.className + ' ').indexOf(' ' + className+ ' ') > -1;
}
Otherwise you will also get true if the class you are looking for is part of another class name.
DEMO
jQuery uses a similar (if not the same) method.
Applied to the example:
As this does not work together with the switch statement, you could achieve the same effect with this code:
var test = document.getElementById("test"),
classes = ['class1', 'class2', 'class3', 'class4'];
test.innerHTML = "";
for(var i = 0, j = classes.length; i < j; i++) {
if(hasClass(test, classes[i])) {
test.innerHTML = "I have " + classes[i];
break;
}
}
It's also less redundant ;)
The easy and effective solution is trying .contains method.
test.classList.contains(testClass);
In modern browsers, you can just use the contains method of Element.classList :
testElement.classList.contains(className)
Demo
var testElement = document.getElementById('test');
console.log({
'main' : testElement.classList.contains('main'),
'cont' : testElement.classList.contains('cont'),
'content' : testElement.classList.contains('content'),
'main-cont' : testElement.classList.contains('main-cont'),
'main-content' : testElement.classList.contains('main-content'),
'main main-content' : testElement.classList.contains('main main-content')
});
<div id="test" class="main main-content content"></div>
Supported browsers
(from CanIUse.com)
Polyfill
If you want to use Element.classList but you also want to support older browsers, consider using this polyfill by Eli Grey.
Element.matches()
element.matches(selectorString)
According to MDN Web Docs:
The Element.matches() method returns true if the element would be selected by the specified selector string; otherwise, returns false.
Therefore, you can use Element.matches() to determine if an element contains a class.
const element = document.querySelector('#example');
console.log(element.matches('.foo')); // true
<div id="example" class="foo bar"></div>
View Browser Compatibility
This question is pretty solidly answered by element.classList.contains(), but people got pretty extravagant with their answers and made some bold claims, so I ran a benchmark.
Remember that each test is doing 1000 iterations, so most of these are still very fast. Unless you rely extensively on this for a specific operation, you won't see a performance difference.
I ran some tests with basically every way to do this. On my machine, (Win 10, 24gb, i7-8700), classList.contains performed super well. So did className.split(' ') which is effectively the same.
The winner though is classList.contains(). If you're not checking for classList to be undefined, ~(' ' + v.className + ' ').indexOf(' ' + classToFind + ' ') creeps ahead 5-15%
Since he wants to use switch(), I'm surprised no one has put this forth yet:
var test = document.getElementById("test");
var testClasses = test.className.split(" ");
test.innerHTML = "";
for(var i=0; i<testClasses.length; i++) {
switch(testClasses[i]) {
case "class1": test.innerHTML += "I have class1<br/>"; break;
case "class2": test.innerHTML += "I have class2<br/>"; break;
case "class3": test.innerHTML += "I have class3<br/>"; break;
case "class4": test.innerHTML += "I have class4<br/>"; break;
default: test.innerHTML += "(unknown class:" + testClasses[i] + ")<br/>";
}
}
Here is a little snippet If you’re trying to check wether element contains a class, without using jQuery.
function hasClass(element, className) {
return element.className && new RegExp("(^|\\s)" + className + "(\\s|$)").test(element.className);
}
This accounts for the fact that element might contain multiple class names separated by space.
OR
You can also assign this function to element prototype.
Element.prototype.hasClass = function(className) {
return this.className && new RegExp("(^|\\s)" + className + "(\\s|$)").test(this.className);
};
And trigger it like this (very similar to jQuery’s .hasClass() function):
document.getElementById('MyDiv').hasClass('active');
className is just a string so you can use the regular indexOf function to see if the list of classes contains another string.
This is a little old, but maybe someone will find my solution helpfull:
// Fix IE's indexOf Array
if (!Array.prototype.indexOf) {
Array.prototype.indexOf = function (searchElement) {
if (this == null) throw new TypeError();
var t = Object(this);
var len = t.length >>> 0;
if (len === 0) return -1;
var n = 0;
if (arguments.length > 0) {
n = Number(arguments[1]);
if (n != n) n = 0;
else if (n != 0 && n != Infinity && n != -Infinity) n = (n > 0 || -1) * Math.floor(Math.abs(n));
}
if (n >= len) return -1;
var k = n >= 0 ? n : Math.max(len - Math.abs(n), 0);
for (; k < len; k++) if (k in t && t[k] === searchElement) return k;
return -1;
}
}
// add hasClass support
if (!Element.prototype.hasClass) {
Element.prototype.hasClass = function (classname) {
if (this == null) throw new TypeError();
return this.className.split(' ').indexOf(classname) === -1 ? false : true;
}
}
A simplified oneliner:1
function hasClassName(classname,id) {
return String ( ( document.getElementById(id)||{} ) .className )
.split(/\s/)
.indexOf(classname) >= 0;
}
1 indexOf for arrays is not supported by IE (ofcourse). There are plenty of monkey patches to be found on the net for that.
I know there a lot of answers but most of these are for additional functions and additional classes. This is the one I personally use; much cleaner and much less lines of code!
if( document.body.className.match('category-page') ) {
console.log('yes');
}
I've created a prototype method which uses classList, if possible, else resorts to indexOf:
Element.prototype.hasClass = Element.prototype.hasClass ||
function(classArr){
var hasClass = 0,
className = this.getAttribute('class');
if( this == null || !classArr || !className ) return false;
if( !(classArr instanceof Array) )
classArr = classArr.split(' ');
for( var i in classArr )
// this.classList.contains(classArr[i]) // for modern browsers
if( className.split(classArr[i]).length > 1 )
hasClass++;
return hasClass == classArr.length;
};
///////////////////////////////
// TESTS (see browser's console when inspecting the output)
var elm1 = document.querySelector('p');
var elm2 = document.querySelector('b');
var elm3 = elm1.firstChild; // textNode
var elm4 = document.querySelector('text'); // SVG text
console.log( elm1, ' has class "a": ', elm1.hasClass('a') );
console.log( elm1, ' has class "b": ', elm1.hasClass('b') );
console.log( elm1, ' has class "c": ', elm1.hasClass('c') );
console.log( elm1, ' has class "d": ', elm1.hasClass('d') );
console.log( elm1, ' has class "a c": ', elm1.hasClass('a c') );
console.log( elm1, ' has class "a d": ', elm1.hasClass('a d') );
console.log( elm1, ' has class "": ', elm1.hasClass('') );
console.log( elm2, ' has class "a": ', elm2.hasClass('a') );
// console.log( elm3, ' has class "a": ', elm3.hasClass('a') );
console.log( elm4, ' has class "a": ', elm4.hasClass('a') );
<p class='a b c'>This is a <b>test</b> string</p>
<svg xmlns="http://www.w3.org/2000/svg" width="100px" height="50px">
<text x="10" y="20" class='a'>SVG Text Example</text>
</svg>
Test page
Here's a case-insensitive trivial solution:
function hasClass(element, classNameToTestFor) {
var classNames = element.className.split(' ');
for (var i = 0; i < classNames.length; i++) {
if (classNames[i].toLowerCase() == classNameToTestFor.toLowerCase()) {
return true;
}
}
return false;
}
Felix's trick of adding spaces to flank the className and the string you're searching for is the right approach to determining whether the elements has the class or not.
To have different behaviour according to the class, you may use function references, or functions, within a map:
function fn1(element){ /* code for element with class1 */ }
function fn2(element){ /* code for element with class2 */ }
function fn2(element){ /* code for element with class3 */ }
var fns={'class1': fn1, 'class2': fn2, 'class3': fn3};
for(var i in fns) {
if(hasClass(test, i)) {
fns[i](test);
}
}
for(var i in fns) iterates through the keys within the fns map.
Having no break after fnsi allows the code to be executed whenever there is a match - so that if the element has, f.i., class1 and class2, both fn1 and fn2 will be executed.
The advantage of this approach is that the code to execute for each class is arbitrary, like the one in the switch statement; in your example all the cases performed a similar operation, but tomorrow you may need to do different things for each.
You may simulate the default case by having a status variable telling whether a match was found in the loop or not.
If the element only has one class name you can quickly check it by getting the class attribute. The other answers are much more robust but this certainly has it's use cases.
if ( element.getAttribute('class') === 'classname' ) {
}
See this Codepen link for faster and easy way of checking an element if it has a specific class using vanilla JavaScript~!
hasClass (Vanilla JS)
function hasClass(element, cls) {
return (' ' + element.className + ' ').indexOf(' ' + cls + ' ') > -1;
}
This is supported on IE8+.
First we check if classList exists if it does we can use the contains method which is supported by IE10+. If we are on IE9 or 8 it falls back to using a regex, which is not as efficient but is a concise polyfill.
if (el.classList) {
el.classList.contains(className);
} else {
new RegExp('(^| )' + className + '( |$)', 'gi').test(el.className);
}
Alternatively if you are compiling with babel you can simply use:
el.classList.contains(className);
To check if an element contains a class, you use the contains() method of the classList property of the element:*
element.classList.contains(className);
*Suppose you have the following element:
<div class="secondary info">Item</div>*
To check if the element contains the secondary class, you use the following code:
const div = document.querySelector('div');
div.classList.contains('secondary'); // true
The following returns false because the element doesn’t have the class error:
const div = document.querySelector('div');
div.classList.contains('error'); // false
I think that perfect solution will be this
if ($(this).hasClass("your_Class"))
alert("positive");
else
alert("Negative");
I would Poly fill the classList functionality and use the new syntax. This way newer browser will use the new implementation (which is much faster) and only old browsers will take the performance hit from the code.
https://github.com/remy/polyfills/blob/master/classList.js
This is a bit off, but if you have an event that triggers switch, you can do without classes:
<div id="classOne1"></div>
<div id="classOne2"></div>
<div id="classTwo3"></div>
You can do
$('body').click( function() {
switch ( this.id.replace(/[0-9]/g, '') ) {
case 'classOne': this.innerHTML = "I have classOne"; break;
case 'classTwo': this.innerHTML = "I have classTwo"; break;
default: this.innerHTML = "";
}
});
.replace(/[0-9]/g, '') removes digits from id.
It is a bit hacky, but works for long switches without extra functions or loops
As the accepted answer suggests, Element.className returns a string, so you can easily check if a class exists by using the indexOf() method:
element.className.indexOf('animated') > -1
If you are interested in the performance difference between indexOf vs classList.contains, using indexOf seems to be slightly faster. I did a quick benchmark performance test to check that. Here are my findings: ClassName.indexOf vs ClassList.contains.
Try this one:
document.getElementsByClassName = function(cl) {
var retnode = [];
var myclass = new RegExp('\\b'+cl+'\\b');
var elem = this.getElementsByTagName('*');
for (var i = 0; i < elem.length; i++) {
var classes = elem[i].className;
if (myclass.test(classes)) retnode.push(elem[i]);
}
return retnode;
};
in which element is currently the class '.bar' ? Here is another solution but it's up to you.
var reg = /Image/g, // regexp for an image element
query = document.querySelector('.bar'); // returns [object HTMLImageElement]
query += this.toString(); // turns object into a string
if (query.match(reg)) { // checks if it matches
alert('the class .bar is attached to the following Element:\n' + query);
}
jsfiddle demo
Of course this is only a lookup for 1 simple element <img>(/Image/g) but you can put all in an array like <li> is /LI/g, <ul> = /UL/g etc.
Just to add to the answer for people trying to find class names within inline SVG elements.
Change the hasCLass() function to:
function hasClass(element, cls) {
return (' ' + element.getAttribute('class') + ' ').indexOf(' ' + cls + ' ') > -1;
}
Instead of using the className property you'll need to use the getAttribute() method to grab the class name.
I created these functions for my website, I use only vanilla javascript, maybe it will help someone.
First I created a function to get any HTML element:
//return an HTML element by ID, class or tag name
var getElement = function(selector) {
var elements = [];
if(selector[0] == '#') {
elements.push(document.getElementById(selector.substring(1, selector.length)));
} else if(selector[0] == '.') {
elements = document.getElementsByClassName(selector.substring(1, selector.length));
} else {
elements = document.getElementsByTagName(selector);
}
return elements;
}
Then the function that recieve the class to remove and the selector of the element:
var hasClass = function(selector, _class) {
var elements = getElement(selector);
var contains = false;
for (let index = 0; index < elements.length; index++) {
const curElement = elements[index];
if(curElement.classList.contains(_class)) {
contains = true;
break;
}
}
return contains;
}
Now you can use it like this:
hasClass('body', 'gray')
hasClass('#like', 'green')
hasClass('.button', 'active')
Hope it will help.
Tip: Try to remove dependencies of jQuery in your projects as much as you can - VanillaJS.
document.firstElementChild returns <html> tag then the classList attribute returns all classes added to it.
if(document.firstElementChild.classList.contains("your-class")){
// <html> has 'your-class'
} else {
// <html> doesn't have 'your-class'
}
Since .className is a string, you can use the string includes() method to check if your .className includes your class name:
element.className.includes("class1")
Using the classList is also ideal
HTML
<div id="box" class="myClass"></div>
JavaScript
const element = document.querySelector("#box");
element.classList.contains("myClass");
For me the most elegant and faster way to achieve it is:
function hasClass(el, cl) {
return el.classList ? el.classList.contains(cl) : !!el.className && !!el.className.match(new RegExp('(?: |^)' + cl + '(?: |$)'));
}