How can I check the existence of an element in jQuery?
The current code that I have is this:
if ($(selector).length > 0) {
// Do something
}
Is there a more elegant way to approach this? Perhaps a plugin or a function?
In JavaScript, everything is 'truthy' or 'falsy', and for numbers 0 means false, everything else true. So you could write:
if ($(selector).length)
You don't need that >0 part.
Yes!
jQuery.fn.exists = function(){ return this.length > 0; }
if ($(selector).exists()) {
// Do something
}
This is in response to: Herding Code podcast with Jeff Atwood
If you used
jQuery.fn.exists = function(){return ($(this).length > 0);}
if ($(selector).exists()) { }
you would imply that chaining was possible when it is not.
This would be better:
jQuery.exists = function(selector) {return ($(selector).length > 0);}
if ($.exists(selector)) { }
Alternatively, from the FAQ:
if ( $('#myDiv').length ) { /* Do something */ }
You could also use the following. If there are no values in the jQuery object array then getting the first item in the array would return undefined.
if ( $('#myDiv')[0] ) { /* Do something */ }
You can use this:
// if element exists
if($('selector').length){ /* do something */ }
// if element does not exist
if(!$('selector').length){ /* do something */ }
The fastest and most semantically self explaining way to check for existence is actually by using plain JavaScript:
if (document.getElementById('element_id')) {
// Do something
}
It is a bit longer to write than the jQuery length alternative, but executes faster since it is a native JS method.
And it is better than the alternative of writing your own jQuery function. That alternative is slower, for the reasons #snover stated. But it would also give other programmers the impression that the exists() function is something inherent to jQuery. JavaScript would/should be understood by others editing your code, without increased knowledge debt.
NB: Notice the lack of an '#' before the element_id (since this is plain JS, not jQuery).
You can save a few bytes by writing:
if ($(selector)[0]) { ... }
This works because each jQuery object also masquerades as an array, so we can use the array dereferencing operator to get the first item from the array. It returns undefined if there is no item at the specified index.
You can use:
if ($(selector).is('*')) {
// Do something
}
A little more elegant, perhaps.
This plugin can be used in an if statement like if ($(ele).exist()) { /* DO WORK */ } or using a callback.
Plugin
;;(function($) {
if (!$.exist) {
$.extend({
exist: function() {
var ele, cbmExist, cbmNotExist;
if (arguments.length) {
for (x in arguments) {
switch (typeof arguments[x]) {
case 'function':
if (typeof cbmExist == "undefined") cbmExist = arguments[x];
else cbmNotExist = arguments[x];
break;
case 'object':
if (arguments[x] instanceof jQuery) ele = arguments[x];
else {
var obj = arguments[x];
for (y in obj) {
if (typeof obj[y] == 'function') {
if (typeof cbmExist == "undefined") cbmExist = obj[y];
else cbmNotExist = obj[y];
}
if (typeof obj[y] == 'object' && obj[y] instanceof jQuery) ele = obj[y];
if (typeof obj[y] == 'string') ele = $(obj[y]);
}
}
break;
case 'string':
ele = $(arguments[x]);
break;
}
}
}
if (typeof cbmExist == 'function') {
var exist = ele.length > 0 ? true : false;
if (exist) {
return ele.each(function(i) { cbmExist.apply(this, [exist, ele, i]); });
}
else if (typeof cbmNotExist == 'function') {
cbmNotExist.apply(ele, [exist, ele]);
return ele;
}
else {
if (ele.length <= 1) return ele.length > 0 ? true : false;
else return ele.length;
}
}
else {
if (ele.length <= 1) return ele.length > 0 ? true : false;
else return ele.length;
}
return false;
}
});
$.fn.extend({
exist: function() {
var args = [$(this)];
if (arguments.length) for (x in arguments) args.push(arguments[x]);
return $.exist.apply($, args);
}
});
}
})(jQuery);
jsFiddle
You may specify one or two callbacks. The first one will fire if the element exists, the second one will fire if the element does not exist. However, if you choose to pass only one function, it will only fire when the element exists. Thus, the chain will die if the selected element does not exist. Of course, if it does exist, the first function will fire and the chain will continue.
Keep in mind that using the callback variant helps maintain chainability – the element is returned and you can continue chaining commands as with any other jQuery method!
Example Uses
if ($.exist('#eleID')) { /* DO WORK */ } // param as STRING
if ($.exist($('#eleID'))) { /* DO WORK */ } // param as jQuery OBJECT
if ($('#eleID').exist()) { /* DO WORK */ } // enduced on jQuery OBJECT
$.exist('#eleID', function() { // param is STRING && CALLBACK METHOD
/* DO WORK */
/* This will ONLY fire if the element EXIST */
}, function() { // param is STRING && CALLBACK METHOD
/* DO WORK */
/* This will ONLY fire if the element DOES NOT EXIST */
})
$('#eleID').exist(function() { // enduced on jQuery OBJECT with CALLBACK METHOD
/* DO WORK */
/* This will ONLY fire if the element EXIST */
})
$.exist({ // param is OBJECT containing 2 key|value pairs: element = STRING, callback = METHOD
element: '#eleID',
callback: function() {
/* DO WORK */
/* This will ONLY fire if the element EXIST */
}
})
I see most of the answers here are not accurate as they should be, they check element length, it can be OK in many cases, but not 100%, imagine if number pass to the function instead, so I prototype a function which check all conditions and return the answer as it should be:
$.fn.exists = $.fn.exists || function() {
return !!(this.length && (this[0] instanceof HTMLDocument || this[0] instanceof HTMLElement));
}
This will check both length and type, Now you can check it this way:
$(1980).exists(); //return false
$([1,2,3]).exists(); //return false
$({name: 'stackoverflow', url: 'http://www.stackoverflow.com'}).exists(); //return false
$([{nodeName: 'foo'}]).exists() // returns false
$('div').exists(); //return true
$('.header').exists(); //return true
$(document).exists(); //return true
$('body').exists(); //return true
There's no need for jQuery really. With plain JavaScript it's easier and semantically correct to check for:
if(document.getElementById("myElement")) {
//Do something...
}
If for any reason you don't want to put an id to the element, you can still use any other JavaScript method designed to access the DOM.
jQuery is really cool, but don't let pure JavaScript fall into oblivion...
You could use this:
jQuery.fn.extend({
exists: function() { return this.length }
});
if($(selector).exists()){/*do something*/}
The reason all of the previous answers require the .length parameter is that they are mostly using jquery's $() selector which has querySelectorAll behind the curtains (or they are using it directly). This method is rather slow because it needs to parse the entire DOM tree looking for all matches to that selector and populating an array with them.
The ['length'] parameter is not needed or useful and the code will be a lot faster if you directly use document.querySelector(selector) instead, because it returns the first element it matches or null if not found.
function elementIfExists(selector){ //named this way on purpose, see below
return document.querySelector(selector);
}
/* usage: */
var myelement = elementIfExists("#myid") || myfallbackelement;
However this method leaves us with the actual object being returned; which is fine if it isn't going to be saved as variable and used repeatedly (thus keeping the reference around if we forget).
var myel=elementIfExists("#myid");
// now we are using a reference to the element which will linger after removal
myel.getParentNode.removeChild(myel);
console.log(elementIfExists("#myid")); /* null */
console.log(myel); /* giant table lingering around detached from document */
myel=null; /* now it can be garbage collected */
In some cases this may be desired. It can be used in a for loop like this:
/* locally scoped myel gets garbage collected even with the break; */
for (var myel; myel = elementIfExist(sel); myel.getParentNode.removeChild(myel))
if (myel == myblacklistedel) break;
If you don't actually need the element and want to get/store just a true/false, just double not it !! It works for shoes that come untied, so why knot here?
function elementExists(selector){
return !!document.querySelector(selector);
}
/* usage: */
var hastables = elementExists("table"); /* will be true or false */
if (hastables){
/* insert css style sheet for our pretty tables */
}
setTimeOut(function (){if (hastables && !elementExists("#mytablecss"))
alert("bad table layouts");},3000);
Is $.contains() what you want?
jQuery.contains( container, contained )
The $.contains() method returns true if the DOM element provided by the second argument is a descendant of the DOM element provided by the first argument, whether it is a direct child or nested more deeply. Otherwise, it returns false. Only element nodes are supported; if the second argument is a text or comment node, $.contains() will return false.
Note: The first argument must be a DOM element, not a jQuery object or plain JavaScript object.
You can check element is present or not using length in java script.
If length is greater than zero then element is present if length is zero then
element is not present
// These by Id
if ($("#elementid").length > 0) {
// Element is Present
} else {
// Element is not Present
}
// These by Class
if ($(".elementClass").length > 0) {
// Element is Present
} else {
// Element is not Present
}
I have found if ($(selector).length) {} to be insufficient. It will silently break your app when selector is an empty object {}.
var $target = $({});
console.log($target, $target.length);
// Console output:
// -------------------------------------
// [▼ Object ] 1
// ► __proto__: Object
My only suggestion is to perform an additional check for {}.
if ($.isEmptyObject(selector) || !$(selector).length) {
throw new Error('Unable to work with the given selector.');
}
I'm still looking for a better solution though as this one is a bit heavy.
Edit: WARNING! This doesn't work in IE when selector is a string.
$.isEmptyObject('hello') // FALSE in Chrome and TRUE in IE
Checking for existence of an element is documented neatly in the official jQuery website itself!
Use the .length property of the jQuery collection returned by your
selector:
if ($("#myDiv").length) {
$("#myDiv").show();
}
Note that it isn't always necessary to test whether an element exists.
The following code will show the element if it exists, and do nothing
(with no errors) if it does not:
$("#myDiv").show();
this is very similar to all of the answers, but why not use the ! operator twice so you can get a boolean:
jQuery.fn.exists = function(){return !!this.length};
if ($(selector).exists()) {
// the element exists, now what?...
}
No need for jQuery (basic solution)
if(document.querySelector('.a-class')) {
// do something
}
Much more performant option below (notice the lack of a dot before a-class).
if(document.getElementsByClassName('a-class')[0]) {
// do something
}
querySelector uses a proper matching engine like $() (sizzle) in jQuery and uses more computing power but in 99% of cases will do just fine. The second option is more explicit and tells the code exactly what to do. It's much faster according to JSBench https://jsbench.me/65l2up3t8i
$(selector).length && //Do something
Try testing for DOM element
if (!!$(selector)[0]) // do stuff
Inspired by hiway's answer I came up with the following:
$.fn.exists = function() {
return $.contains( document.documentElement, this[0] );
}
jQuery.contains takes two DOM elements and checks whether the first one contains the second one.
Using document.documentElement as the first argument fulfills the semantics of the exists method when we want to apply it solely to check the existence of an element in the current document.
Below, I've put together a snippet that compares jQuery.exists() against the $(sel)[0] and $(sel).length approaches which both return truthy values for $(4) while $(4).exists() returns false. In the context of checking for existence of an element in the DOM this seems to be the desired result.
$.fn.exists = function() {
return $.contains(document.documentElement, this[0]);
}
var testFuncs = [
function(jq) { return !!jq[0]; },
function(jq) { return !!jq.length; },
function(jq) { return jq.exists(); },
];
var inputs = [
["$()",$()],
["$(4)",$(4)],
["$('#idoexist')",$('#idoexist')],
["$('#idontexist')",$('#idontexist')]
];
for( var i = 0, l = inputs.length, tr, input; i < l; i++ ) {
input = inputs[i][1];
tr = "<tr><td>" + inputs[i][0] + "</td><td>"
+ testFuncs[0](input) + "</td><td>"
+ testFuncs[1](input) + "</td><td>"
+ testFuncs[2](input) + "</td></tr>";
$("table").append(tr);
}
td { border: 1px solid black }
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="idoexist">#idoexist</div>
<table style>
<tr>
<td>Input</td><td>!!$(sel)[0]</td><td>!!$(sel).length</td><td>$(sel).exists()</td>
</tr>
</table>
<script>
$.fn.exists = function() {
return $.contains(document.documentElement, this[0]);
}
</script>
I just like to use plain vanilla javascript to do this.
function isExists(selector){
return document.querySelectorAll(selector).length>0;
}
I stumbled upon this question and i'd like to share a snippet of code i currently use:
$.fn.exists = function(callback) {
var self = this;
var wrapper = (function(){
function notExists () {}
notExists.prototype.otherwise = function(fallback){
if (!self.length) {
fallback.call();
}
};
return new notExists;
})();
if(self.length) {
callback.call();
}
return wrapper;
}
And now i can write code like this -
$("#elem").exists(function(){
alert ("it exists");
}).otherwise(function(){
alert ("it doesn't exist");
});
It might seem a lot of code, but when written in CoffeeScript it is quite small:
$.fn.exists = (callback) ->
exists = #length
callback.call() if exists
new class
otherwise: (fallback) ->
fallback.call() if not exists
I had a case where I wanted to see if an object exists inside of another so I added something to the first answer to check for a selector inside the selector..
// Checks if an object exists.
// Usage:
//
// $(selector).exists()
//
// Or:
//
// $(selector).exists(anotherSelector);
jQuery.fn.exists = function(selector) {
return selector ? this.find(selector).length : this.length;
};
How about:
function exists(selector) {
return $(selector).length;
}
if (exists(selector)) {
// do something
}
It's very minimal and saves you having to enclose the selector with $() every time.
I'm using this:
$.fn.ifExists = function(fn) {
if (this.length) {
$(fn(this));
}
};
$("#element").ifExists(
function($this){
$this.addClass('someClass').animate({marginTop:20},function(){alert('ok')});
}
);
Execute the chain only if a jQuery element exist - http://jsfiddle.net/andres_314/vbNM3/2/
$("selector") returns an object which has the length property. If the selector finds any elements, they will be included in the object. So if you check its length you can see if any elements exist. In JavaScript 0 == false, so if you don't get 0 your code will run.
if($("selector").length){
//code in the case
}
Here is my favorite exist method in jQuery
$.fn.exist = function(callback) {
return $(this).each(function () {
var target = $(this);
if (this.length > 0 && typeof callback === 'function') {
callback.call(target);
}
});
};
and other version which supports callback when selector does not exist
$.fn.exist = function(onExist, onNotExist) {
return $(this).each(function() {
var target = $(this);
if (this.length > 0) {
if (typeof onExist === 'function') {
onExist.call(target);
}
} else {
if (typeof onNotExist === 'function') {
onNotExist.call(target);
}
}
});
};
Example:
$('#foo .bar').exist(
function () {
// Stuff when '#foo .bar' exists
},
function () {
// Stuff when '#foo .bar' does not exist
}
);
You don't have to check if it's greater than 0 like $(selector).length > 0, $(selector).length it's enough and an elegant way to check the existence of elements. I don't think that it is worth to write a function only for this, if you want to do more extra things, then yes.
if($(selector).length){
// true if length is not 0
} else {
// false if length is 0
}
Here is the complete example of different situations and way to check if element exists using direct if on jQuery selector may or may not work because it returns array or elements.
var a = null;
var b = []
var c = undefined ;
if(a) { console.log(" a exist")} else { console.log("a doesn't exit")}
// output: a doesn't exit
if(b) { console.log(" b exist")} else { console.log("b doesn't exit")}
// output: b exist
if(c) { console.log(" c exist")} else { console.log("c doesn't exit")}
// output: c doesn't exit
FINAL SOLUTION
if($("#xysyxxs").length){ console.log("xusyxxs exist")} else { console.log("xusyxxs doesnn't exist") }
//output : xusyxxs doesnn't exist
if($(".xysyxxs").length){ console.log("xusyxxs exist")} else { console.log("xusyxxs doesnn't exist") }
//output : xusyxxs doesnn't exist
Demo
console.log("existing id", $('#id-1').length)
console.log("non existing id", $('#id-2').length)
console.log("existing class single instance", $('.cls-1').length)
console.log("existing class multiple instance", $('.cls-2').length)
console.log("non existing class", $('.cls-3').length)
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div id="id-1">
<div class="cls-1 cls-2"></div>
<div class="cls-2"></div>
</div>
In an API response, I want to check if a variable exists. If it doesn't, I want to assign it a blank value:
if(!data3.fields[i+2].values.value[0]) {
data3.fields[i+2].values.value[0] = "";
} else {
break;
}
Error in the console is:
Uncaught TypeError: Cannot read property 'value' of undefined
This confuses me because I thought that's exactly what my if the statement was checking. Any ideas what's going on here?
The if check won't protect you from trying to use an undefined variable. In your instance the values property is undefined. If you wanted to test for that you would need to first check that specific property
if(data3.fields[i+2].values !== undefined && data3.fields[i+2].values.value[0]){
//do something with data3.fields[i+2].values.value[0]
}
additionally, if you are in a scenario where you don't even know if data3 exists (for example you are checking for the existence of a third party script, or something else in your environment) you would need to use the typeof operator to be safe. E.G.
if(typeof(ga) !== 'undefined'){ //typeof returns a string. This would be testing for google analytics on a page.
It doesnt work like PHP does (which checks the whole 'chain'). In your example, you actually check if .value[0] of values exists, but dont check if values exists. The full version should be:
if( data3 && && data3.fields[i+2] && data3.fields[i+2].values && !data3.fields[i+2].values.value[0]) {}
In your code ata3.fields[i+2].values is undefined, and you're trying to access value[0] of 'undefined'
Or slightly more simplefied, if you wand to test if d has a value, you have to make sure that a, b and c aldo have a value:
if( a && a.b && a.b.c && !a.b.c.d){ /* ... */ }
You can remove checks on the left side of the checks if you are sure those exist. E.g.: If you know that a.b always exist, you can simplefy:
if( a.b.c && !a.b.c.d){ /* ... */ }
If you really want to make sure the complete property chain is not undefined you have to check every single step and the later ones won't be executed if at least && condition is false.
if (data3 && data3.fields && data3.fields[i+2] && data3.fields[i+2].values && data3.fields[i+2].values.value && data3.fields[i + 2].values.value[0]) {
data3.fields[i + 2].values.value[0] = "";
} else {
break;
}
Another way would be to just do it and catch the exception:
try {
data3.fields[i + 2].values.value[0] = "";
} catch (e) {
break;
}
The error is telling you that data3.fields[i+2].values is undefined. You can't check for a property .value on undefined.
You'd need to verify each property/index belongs along the way if you always want that nested path to default to an empty string.
if (data3.fields[i+2] === undefined) {
data.fields[i+2] = {};
}
if (data3.fields[i+2].values === undefined) {
data3.fields[i+2].values = {};
}
if (data3.fields[i+2].values.value === undefined) {
data3.fields[i+2].values.value = [];
}
// and finally your empty string assignment
if (data3.fields[i+2].values.value[0] === undefined) {
data3.fields[i+2].values.value[0] = '';
}
Depending on your requirements, you might be able to get away with assigning a stub as soon as you know data3.fields[i+2] is undefined.
if (data3.fields[i+2] === undefined) {
data3.fields[i+2] = {
values: {
value: ['']
}
};
}
I am having trouble using the textInput binding with a custom autocomplete/dropdown function. I am using the textInput binding so I do see the view model get updated, but the update takes place after the keypress event which is what my autocomplete is bound too. Here is my autocomplete function:
$("#table-body").on("keypress", ".combo", function (e) {
var item = ko.dataFor(e.target),
drop = $(".dropdown-menu", this);
if (item.Name() !== undefined && item.Name().length === 0) {
$(".input-group-btn", this).removeClass("open");
} else if (item.Name() !== undefined && item.Name() !== null && item.Name() !== "") {
drop.children().not(":containsNoCase(" + item.Name() + ")").hide();
drop.children().filter(":containsNoCase(" + item.Name() + ")").show();
$(".input-group-btn", this).addClass("open");
}
});
In the event above, item.Name() is null or whitespace when the first character is entered, and then is always 1 character behind what is typed. Any ideas on how I can change the event capture to be after the textInput has updated the view model?
It's interesting that the update of the model value takes so long and gets set so late in the game. I looked at the textInput binding source and found that knockout defers the setting of the value by 4ms when the input is changed. Might explain why the value is not updated at the time the handler is run?
var deferUpdateModel = function (event) {
if (!timeoutHandle) {
// The elementValueBeforeEvent variable is set *only* during the brief gap between an
// event firing and the updateModel function running. This allows us to ignore model
// updates that are from the previous state of the element, usually due to techniques
// such as rateLimit. Such updates, if not ignored, can cause keystrokes to be lost.
elementValueBeforeEvent = element.value;
var handler = DEBUG ? updateModel.bind(element, {type: event.type}) : updateModel;
timeoutHandle = setTimeout(handler, 4);
}
};
Instead of manually binding to the keypress event, I would consider using a knockout subscription on your Name observable. By doing do, you can be assured that you have the latest value and won't have to worry about the 1-behind problem. Whipped up a quick fiddle to demonstrate.
vm.name.subscribe(function(val){
var name = val,
drop = $(".dropdown-menu");
if (name !== undefined && name.length === 0) {
$(".input-group-btn").removeClass("open");
} else if (name !== undefined && name !== null && name !== "") {
drop.children().not(":contains(" + name + ")").hide();
drop.children().filter(":contains(" + name + ")").show();
$(".input-group-btn").addClass("open");
}
});
http://jsfiddle.net/ttz0p33n/
I have a textarea where I use javascript to check if there's something writen on it:
if (!editorInstance.document.getBody().getChild(0).getText()) {
do some action
}
It works fine for firefox, but in IE9 I get this error telling it's a null or undefined object (so IE doesnt check my condition).
so I tried:
var hasText = editorInstance.document.getBody().getChild(0).getText();
if (typeof hasText === 'undefined') {
do some action
}
The problem is that it still stops in the first line ( var hasText = edit... ), because the editorInstance.document.getBody().getChild(0).getText() returns null or undefined
EDIT
when I do editorInstance.document.getBody().getChild(0).getText(), I get all text entered in the textarea, but when there's no text entered (I check it to validate this field), this code returns nothing, this is why the hasText variable is not working the way I expected.
Any idea about how can I solve it?
You need to check for the presence of each variable and function result that you refer to.
var firstChild = editorInstance && editorInstance.document && editorInstance.document.getBody() && editorInstance.document.getBody().getChild(0);
if (!firstChild || firstChild.getText() === '') {
// do some action
}
&& is Javascript's logical AND operator. It’s very handy for cases like this, when you want to fetch an object's value, but the object itself might be null or undefined.
Consider the following statement:
var doc = editorInstance && editorInstance.document;
It means the same as
var doc;
if (editorInstance) {
doc = editorInstance.document;
} else {
doc = editorInstance;
}
but it's shorter. This statement will not error out if editorInstance is null.
function test() {
var editor_val1 = CKEDITOR.instances.id1.document.getBody().getChild(0).getText() ;
var editor_val2 = CKEDITOR.instances.id2.document.getBody().getChild(0).getText() ;
var editor_val3 = CKEDITOR.instances.id3.document.getBody().getChild(0).getText() ;
if ((editor_val1 == '') || (editor_val2 == '') || (editor_val3 == '')) {
alert('Editor value cannot be empty!') ;
return false ;
}
return true ;
}
Here is the line which is causing null or not an object error
if(frm.elements["hdn_retain"+indexval].value==""){
....
} else {
....
}
frm.elements["hdn_retain"+indexval] may be a null object. So, it will have error when getting the value. You can check the frm.elements["hdn_retain"+indexval] if it is null first.
if(frm.elements["hdn_retain"+indexval] != null && frm.elements["hdn_retain"+indexval].value=="")
Either frm or frm.elements["hdn_retain"+indexval] isn't a valid object (doesn't exist in the dom) and therefore you can't access it's property.
you could try something like:
if(frm.elements["hdn_retain"+indexval] && frm.elements["hdn_retain"+indexval].value==""){
Following is the result of alert statement:
alert("frm:::"+frm);
alert("frm elements::::"+frm.elements);
alert("frm hdn_retain :: "+frm.elements["hdn_retain"+indexval]);
frm:::[object]
frm elements::::[object]
frm hdn_retain :: undefined
you can use this utility method getProperty i always use to make sure i get a nested namespace back without worrying about whether or not something is defined:
function getProperty(ns, obj) {
var nsArray = ns.split('.'),
i = 0,
nsLen = nsArray.length;
while (nsLen > 0) {
var newNs = nsArray.shift();
if (obj[newNs]) {
obj = obj[newNs];
} else {
return false;
}
nsLen = nsArray.length;
}
return obj;
};
var index = "hdn_retain" + indexval;
// the following `value` will come back as a valid object/value or a false
value = getProperty('elements.' + index + '.value', frm);
if (value) {
// do whatever
} else {
// do not whatever
}
this can be applied not only to this situation but to any other situation you need to make sure a certain namespace is available before usage.