Questions tagged [javascript]
For questions regarding programming in ECMAScript (JavaScript/JS) and its various dialects/implementations (excluding ActionScript). Note JavaScript is NOT the same as Java! Please include all relevant tags on your question; e.g., [node.js], [jquery], [json], [reactjs], [angular], [ember.js], [vue.js], [typescript], [svelte], etc.
2,359,110
questions
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answers
9.8m
views
How can I remove a specific item from an array?
How do I remove a specific value from an array? Something like:
array.remove(value); // removes all elements with value
I have to use core JavaScript. Frameworks are not allowed.
- 116k
8344
votes
63
answers
3.0m
views
How do I check if an element is hidden in jQuery?
Is it possible to toggle the visibility of an element, using the functions .hide(), .show() or .toggle()?
How would you test if an element is visible or hidden?
- 125k
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votes
29
answers
1.2m
views
What does "use strict" do in JavaScript, and what is the reasoning behind it?
Recently, I ran some of my JavaScript code through Crockford's JSLint, and it gave the following error:
Problem at line 1 character 1: Missing "use strict" statement.
Doing some searching, I ...
- 93.4k
7710
votes
58
answers
7.2m
views
How do I redirect to another webpage?
How can I redirect the user from one page to another using jQuery or pure JavaScript?
- 102k
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votes
86
answers
1.6m
views
How do JavaScript closures work?
How would you explain JavaScript closures to someone with a knowledge of the concepts they consist of (for example functions, variables and the like), but does not understand closures themselves?
I ...
7417
votes
3
answers
7.1m
views
How to check whether a string contains a substring in JavaScript?
Usually I would expect a String.contains() method, but there doesn't seem to be one.
What is a reasonable way to check for this?
7388
votes
41
answers
1.1m
views
var functionName = function() {} vs function functionName() {}
I've recently started maintaining someone else's JavaScript code. I'm fixing bugs, adding features and also trying to tidy up the code and make it more consistent.
The previous developer used two ...
- 85.2k
6964
votes
33
answers
2.8m
views
How do I remove a property from a JavaScript object?
Say I create an object as follows:
let myObject = {
"ircEvent": "PRIVMSG",
"method": "newURI",
"regex": "^http://.*"
};
How should I ...
- 91.2k
6329
votes
43
answers
1.9m
views
How to return the response from an asynchronous call
I have a function foo which makes an asynchronous request. How can I return the response/result from foo?
I am trying to return the value from the callback, as well as assigning the result to a local ...
- 750k
5928
votes
68
answers
3.9m
views
How do I include a JavaScript file in another JavaScript file?
Is there something in JavaScript similar to @import in CSS that allows you to include a JavaScript file inside another JavaScript file?
- 89.5k
5685
votes
37
answers
1.9m
views
What's the difference between using "let" and "var"?
ECMAScript 6 introduced the let statement.
I've heard that it's described as a local variable, but I'm still not quite sure how it behaves differently than the var keyword.
What are the differences? ...
- 102k
5656
votes
48
answers
2.0m
views
Which equals operator (== vs ===) should be used in JavaScript comparisons?
I'm using JSLint to go through JavaScript, and it's returning many suggestions to replace == (two equals signs) with === (three equals signs) when doing things like comparing idSele_UNVEHtype.value....
- 57.4k
5319
votes
40
answers
4.9m
views
For-each over an array in JavaScript
How can I loop through all the entries in an array using JavaScript?
- 55.2k
5256
votes
103
answers
4.0m
views
What's the best way to validate an email address in JavaScript?
What's the best way to validate an email address in JavaScript with a regular expression?
5173
votes
67
answers
2.5m
views
What is the most efficient way to deep clone an object in JavaScript?
What is the most efficient way to clone a JavaScript object? I've seen obj = eval(uneval(o)); being used, but that's non-standard and only supported by Firefox. I've done things like obj = JSON.parse(...
5127
votes
79
answers
4.1m
views
How to replace all occurrences of a string in JavaScript
I have this string in my JavaScript code:
"Test abc test test abc test test test abc test test abc"
Doing:
str = str.replace('abc', '');
Seems to only remove the first occurrence of abc in ...
- 248k
4989
votes
66
answers
4.5m
views
How do I check whether a checkbox is checked in jQuery?
I need to check the checked property of a checkbox and perform an action based on the checked property using jQuery.
For example, if the age checkbox is checked, then I need to show a textbox to enter ...
4876
votes
69
answers
2.5m
views
How to create a GUID / UUID
I'm trying to create globally-unique identifiers in JavaScript. I'm not sure what routines are available on all browsers, how "random" and seeded the built-in random number generator is, ...
4593
votes
56
answers
3.1m
views
How do I check if an array includes a value in JavaScript?
What is the most concise and efficient way to find out if a JavaScript array contains a value?
This is the only way I know to do it:
function contains(a, obj) {
for (var i = 0; i < a.length; i++...
- 70.5k
4574
votes
117
answers
3.0m
views
How do I make the first letter of a string uppercase in JavaScript?
How do I make the first letter of a string uppercase, but not change the case of any of the other letters?
For example:
"this is a test" → "This is a test"
"the Eiffel Tower&...
- 46.4k
4510
votes
15
answers
847k
views
"Thinking in AngularJS" if I have a jQuery background? [closed]
Suppose I'm familiar with developing client-side applications in jQuery, but now I'd like to start using AngularJS. Can you describe the paradigm shift that is necessary? Here are a few questions that ...
- 356k
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votes
41
answers
3.5m
views
How do you get a timestamp in JavaScript?
Something similar to Unix's timestamp, that is a single number that represents the current time and date. Either as a number or a string.
- 265k
4436
votes
43
answers
3.6m
views
Setting "checked" for a checkbox with jQuery
I'd like to do something like this to tick a checkbox using jQuery:
$(".myCheckBox").checked(true);
or
$(".myCheckBox").selected(true);
Does such a thing exist?
- 54.6k
4333
votes
8
answers
570k
views
Why does Google prepend while(1); to their JSON responses?
Why does Google prepend while(1); to their (private) JSON responses?
For example, here's a response while turning a calendar on and off in Google Calendar:
while (1);
[
['u', [
['smsSentFlag', ...
- 40.9k
4319
votes
55
answers
2.4m
views
Which "href" value should I use for JavaScript links, "#" or "javascript:void(0)"?
The following are two methods of building a link that has the sole purpose of running JavaScript code. Which is better, in terms of functionality, page load speed, validation purposes, etc.?
...
4079
votes
68
answers
2.5m
views
How do I copy to the clipboard in JavaScript?
What is the best way to copy text to the clipboard (multi-browser)?
I have tried:
function copyToClipboard(text) {
if (window.clipboardData) { // Internet Explorer
window.clipboardData....
- 44.5k
3898
votes
49
answers
3.5m
views
How do I test for an empty JavaScript object?
After an AJAX request, sometimes my application may return an empty object, like:
var a = {};
How can I check whether that's the case?
- 39.4k
3809
votes
39
answers
774k
views
What is the !! (not not) operator in JavaScript?
I saw some code that seems to use an operator I don't recognize, in the form of two exclamation points, like so: !!. Can someone please tell me what this operator does?
The context in which I saw ...
- 40.6k
3750
votes
25
answers
2.8m
views
How to insert an item into an array at a specific index (JavaScript)
I am looking for a JavaScript array insert method, in the style of:
arr.insert(index, item)
Preferably in jQuery, but any JavaScript implementation will do at this point.
- 76.1k
3696
votes
44
answers
4.6m
views
Loop through an array in JavaScript
In Java you can use a for loop to traverse objects in an array as follows:
String[] myStringArray = {"Hello", "World"};
for (String s : myStringArray)
{
// Do something
}
Can you do the same in ...
- 53.2k
3683
votes
29
answers
2.9m
views
Checking if a key exists in a JavaScript object?
How do I check if a particular key exists in a JavaScript object or array?
If a key doesn't exist, and I try to access it, will it return false? Or throw an error?
- 49.1k
3608
votes
55
answers
2.4m
views
Sort array of objects by string property value
I have an array of JavaScript objects:
var objs = [
{ first_nom: 'Lazslo', last_nom: 'Jamf' },
{ first_nom: 'Pig', last_nom: 'Bodine' },
{ first_nom: 'Pirate', last_nom: '...
- 36.4k
3586
votes
88
answers
3.5m
views
How to round to at most 2 decimal places, if necessary?
I'd like to round at most 2 decimal places, but only if necessary.
Input:
10
1.7777777
9.1
Output:
10
1.78
9.1
How can I do this in JavaScript?
- 38.7k
3558
votes
59
answers
4.4m
views
How can I check for an empty/undefined/null string in JavaScript?
I saw this question, but I didn't see a JavaScript specific example. Is there a simple string.Empty available in JavaScript, or is it just a case of checking for ""?
- 63.7k
3479
votes
76
answers
2.2m
views
How do I correctly clone a JavaScript object?
I have an object x. I'd like to copy it as object y, such that changes to y do not modify x. I realized that copying objects derived from built-in JavaScript objects will result in extra, unwanted ...
- 36.7k
3446
votes
26
answers
3.3m
views
Get the current URL with JavaScript?
All I want is to get the website URL. Not the URL as taken from a link. On the page loading I need to be able to grab the full, current URL of the website and set it as a variable to do with as I ...
dougoftheabaci
3352
votes
44
answers
2.5m
views
How do I loop through or enumerate a JavaScript object?
I have a JavaScript object like the following:
var p = {
"p1": "value1",
"p2": "value2",
"p3": "value3"
};
Now I want to loop through all p elements (p1, p2, p3...) And get their keys ...
- 41.7k
3323
votes
25
answers
771k
views
What is the difference between call and apply?
What is the difference between using Function.prototype.apply() and Function.prototype.call() to invoke a function?
var func = function() {
alert('hello!');
};
func.apply(); vs func.call();
Are ...
- 36.7k
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votes
51
answers
1.9m
views
How can I check if an object is an array? [duplicate]
I'm trying to write a function that either accepts a list of strings, or a single string. If it's a string, then I want to convert it to an array with just the one item so I can loop over it without ...
- 253k
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votes
34
answers
3.1m
views
How can I change an element's class with JavaScript?
How can I change the class of an HTML element in response to an onclick or any other events using JavaScript?
- 34.7k
3158
votes
14
answers
905k
views
event.preventDefault() vs. return false
When I want to prevent other event handlers from executing after a certain event is fired, I can use one of two techniques. I'll use jQuery in the examples, but this applies to plain-JS as well:
1. ...
- 67.8k
3149
votes
88
answers
3.8m
views
What is the JavaScript version of sleep()?
Is there a better way to engineer a sleep in JavaScript than the following pausecomp function (taken from here)?
function pausecomp(millis)
{
var date = new Date();
var curDate = null;
do ...
3140
votes
98
answers
2.8m
views
How can I convert a string to boolean in JavaScript?
Can I convert a string representing a boolean value (e.g., 'true', 'false') into a intrinsic type in JavaScript?
I have a hidden form in HTML that is updated based upon a user's selection within a ...
3135
votes
43
answers
2.0m
views
Creating multiline strings in JavaScript
I have the following code in Ruby. I want to convert this code into JavaScript. What is the equivalent code in JS?
text = <<"HERE"
This
Is
A
Multiline
String
HERE
- 36.2k
3101
votes
50
answers
1.4m
views
Detecting an undefined object property
What's the best way of checking if an object property in JavaScript is undefined?
- 113k
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votes
44
answers
446k
views
JavaScript closure inside loops – simple practical example
var funcs = [];
// let's create 3 functions
for (var i = 0; i < 3; i++) {
// and store them in funcs
funcs[i] = function() {
// each should log its value.
console.log("My value: " + i);
...
- 517k
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votes
34
answers
1.4m
views
How can I upload files asynchronously with jQuery?
I would like to upload a file asynchronously with jQuery.
$(document).ready(function () {
$("#uploadbutton").click(function () {
var filename = $("#file").val();
$.ajax({...
- 74.1k
3045
votes
20
answers
280k
views
Is it possible to apply CSS to half of a character?
What I am looking for:
A way to style one HALF of a character. (In this case, half the letter being transparent)
What I have currently searched for and tried (With no luck):
Methods for styling ...
- 24.2k
3028
votes
62
answers
5.4m
views
How to format a JavaScript date
In JavaScript, how can I format a date object to print as 10-Aug-2010?
- 176k
3018
votes
29
answers
1.4m
views
pretty-print JSON using JavaScript
How can I display JSON in an easy-to-read (for human readers) format? I'm looking primarily for indentation and whitespace, with perhaps even colors / font-styles / etc.
- 61.8k