Develop Reference

How to check when input value is changed?

How can i check when a value on input is changed.
I have a calendar and when i click on calendar it changes the value on input , but when im trying to see if it has changed its not working. i have tried AddEventListener, also jquery on change, also i sent a function on change to call it but none of them is working.
<input type="text" id="date" class="date" onchange="changed()" name="" >
function changed(){
alert("hello world");
}
Main js file for creating the calendar :
This function creates the calendar on my php file .
And then when on click it gets the value on the input with id #date
But When im trying to see if value has changed it is not working .
// Initialize the calendar by appending the HTML dates
function init_calendar(date) {
$(".tbody").empty();
$(".events-container").empty();
var calendar_days = $(".tbody");
var month = date.getMonth();
var year = date.getFullYear();
var day_count = days_in_month(month, year);
var row = $("<tr class='table-row'></tr>");
var today = date.getDate();
// Set date to 1 to find the first day of the month
date.setDate(1);
var first_day = date.getDay();
// 35+firstDay is the number of date elements to be added to the dates table
// 35 is from (7 days in a week) * (up to 5 rows of dates in a month)
for(var i=0; i<35+first_day; i++) {
// Since some of the elements will be blank,
// need to calculate actual date from index
var day = i-first_day+1;
// If it is a sunday, make a new row
if(i%7===0) {
calendar_days.append(row);
row = $("<tr class='table-row'></tr>");
}
// if current index isn't a day in this month, make it blank
if(i < first_day || day > day_count) {
var curr_date = $("<td class='table-date nil'>"+"</td>");
row.append(curr_date);
}
else {
var monthplusone = months[month];
var curr_date = $("<td class='table-date' id='"+day+"-"+monthplusone+"-"+year+"'>"+day+"</td>");
var events = check_events(day, month+1, year);
if(today===day && $(".active-date").length===0) {
curr_date.addClass("active-date");
let x = document.getElementById('date').value=day+"-"+monthplusone+"-"+year;
$('.table-date').ready(function () {
x.value;
});
show_events(events, months[month], day);
}
// If this date has any events, style it with .event-date
if(events.length!==0) {
curr_date.addClass("event-date");
}
// Set onClick handler for clicking a date
$('.table-date').on('click', function () {
document.getElementById('date').value = $(this).attr('id');
});
curr_date.click({events: events, month: months[month], day:day}, date_click);
row.append(curr_date);
}
}
// Append the last row and set the current year
calendar_days.append(row);
$(".year").text(year);
}

Notice that change is actually triggered when the input is not focused anymore.
document.getElementById("date").addEventListener("change", function () {
alert("hello world");
});
<input type="text" id="date" class="date" name="">

This works. Not sure where you're running into an issue.
function changed(){
console.log("hello world");
}
<input type="text" id="date" class="date" onchange="changed()" name="" >
EDIT: Shortened version of init_calender() for others interested in answering:
function setDate() {
document.getElementById("date").value = '19-Dec-2021'
}

I basically agree with #Spankied in that you should try and shorten your code to the point where you are having the issue. However, after looking at your code it seems to me that you want the following function
$('.table-date').on('click', function () {
document.getElementById('date').value = $(this).attr('id');
});
to not only change the value in your #date input but also trigger its change event-handler function. You can do that by changing it to something like
$('.table-date').on('click', function () {
document.getElementById('date').value = $(this).attr('id');
$("#date" ).change();
});
jQuery.change() without any arguments will trigger a predefined "change"-event on the DOM-object that is selected by the jQuery-object.

You can use js to do that:
let x = $(...) //select the input box
let val = x.value;
function repeat() {
if (val !== x.value) {
change()
}
}
setInterval(repeat, 100)
This checks if the result is the same.

This might make your site a bit slow and it might look odd but this will work in just every case
<script>
let Oldvalue = $('.date')[0].val();
setInterval(() => {
let currentValue = $('.data')[0].val()
if (Oldvalue != currentValue){
//do whatever but in end write this
Oldvalue = currentValue;
}
}, 10);
</script>

Stuck on incrementing date in JavaScript

I am trying to create a page that grabs a set of PDFs sorted by date. I can't seem to increment the date correctly. I'm not sure what's going wrong here. I rewrote the code twice now. No luck.
The current issue is that the set variables for the date do not keep the value of the date as a whole. IE incrementing from 12, 31, 2018, or in the case of the URL format 20181231, should result urlIncremented=20190101. January 1st, 2019, but the result of my code is urlIncremented=20181232.
The end result of one loop if set to June 8th 2018, should be: url20180608
I've searched for advice on here, and found a JS file called Date.JS; I've imported it and it was looking promising but just consoles out a part of its code, namely:
function () {
if (this._isSecond) {
this._isSecond=false;
return this;
}
if (this._same) {
this._same=this._is=false;
var o1=this.toObject(),
o2=(arguments[0] || new Date()).toObject(),
v="",
k=j.toLowerCase();
for (var m=(px.length-1); m>-1; m--) {
v=px[m].toLowerCase();
if (o1[v]!=o2[v]) {
return false;
}
if (k==v) {
break;
}
}
return true;
}
if (j.substring(j.length-1)!="s") {
j+="s";
}
return this["add"+j](this._orient);
}
Just a heads up I do not yet know jQuery, I was just playing with it to see if it would help..
Here is my actual code.
let url = "blank",
firstRun = true;
/*
function setDateByIncrement(currentSetDate){
let newDate,
currentDate = new Date(),
day = currentDate.getDate()+1,
month = currentDate.getMonth() + 1,
year = currentDate.getFullYear();
console.log(newDate);
newDate = (year+month+day);
console.log(newDate);
return newDate;
}
*/
// use on First run to set the url and date.
//3
function setURL(){
let urlIncremented = url + dateIncrementMethod();
return urlIncremented;
}
// will open x number of new windows containing URL
//2
function grabOpenPDF(maxNumberDays){
let urlSet = setURL();
//Set the variable for max days.
for(let x = 0; x < maxNumberDays; x++){
//window.open(urlSet);
console.log("It works: " + x);
urlSet = setURL();
}
}
/* TODO Add automatic download for MASS print.
function downloadPDF(){
}
*/
//Starts the task.
//1
function start(load){
console.log("Current Address: " + url);
if(load === 1){
console.log("Event load active. ");
let maxDay = document.querySelector('#maxNumberDays').value;;
grabOpenPDF(maxDay);
}else{
console.log("Event load skip. ")
let maxDay = document.getElementById('maxNumberDays').value;
}
}
//4
function dateIncrementMethod(current){
let dateIncrement;
if(firstRun=== true){
var today = new Date($('#date-input').val());
console.log("FirstRun check in 4. ")
}
firstRun = false;
var tomorrow = today.add(1).day;
console.log(tomorrow);
return tomorrow;
}
/* Possibly Deprecated
//let dateIncrement;
let date = new Date($('#date-input').val());
console.log(date);
day = date.getDate() + 1;
if(firstRun === true){
month = date.getMonth() + 1;
year = date.getFullYear();
//dateIncrement = (parseToAPI(year, month, day));
firstRun = false;
parseToAPI(year, month, day);
}else{
day = date.getDate()+1;
parseToAPI(year, month, day);
}
}
*/
function parseToAPI(year, month, day){
let apiDate;
console.log("Entered parse");
this.day = day;
this.month = month;
let d = this.day.toString(),
m = this.month.toString();
if(d.length === 1){
console.log("Entered First IF");
this.day = ('0') + day;
//console.log(day);
}
if(m.length === 1){
console.log("Entered Second IF")
this.month = ('0') + month;
}
apiDate = (year + "" + "" + month + "" + day);
console.log(apiDate);
return apiDate;
}
<!DOCTYPE html>
<html>
<script src="https://code.jquery.com/jquery-2.0.3.js"></script>
<script src="https://doc-0k-6g-docs.googleusercontent.com/docs/securesc/77gdpvi38k94jj7nmfcm2n3tq7a0ifhu/ehjuusajghqnne5r2ncfvj30cmbll20p/1545105600000/17500114768188980350/17500114768188980350/1CDff-uWGahZX7aLt6WQfV1-R5PFHwiK8?e=download&nonce=52qkphatg2scm&user=17500114768188980350&hash=3uc9iql9m90vcrv3a7mhg8fdjce1b4fe.js"></script>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width">
<title>JS Bin</title>
</head>
<body>
<input type="date" id="date-input" required />
<input type="maxNumberDays" id="maxNumberDays" max="31" required />
<button id="startPDFApp" onClick="start()">Print PDFs</button>
<button id="startPDFApp" onClick="start(1)">Load PDFs</button>
<div id="info"></div>
</body>
</html>

While I haven't invested enough time trying to understand what you're really trying to do, it seems like there's a lot of unnecessary code. I'll leave it to you to decipher what you need.
I can only express that the below code is in an in-between state. It includes a number of changes, most of which I'll point out, but I didn't want to change it too drastically that it all looked foreign. So even the code below has much to be improved on.
Significant changes include:
Because your URL is increasing by one, you may benefit by using a function generator. Inside it increases the date by calling setDate on itself using it's own date + 1. It also uses a string function, padStart, to ensure months and days are always two-digit.
Getting rid of firstRun variable as it is no longer needed
Inside your grabOpenPDF, all you need to do is get the next value returned by the URL generator function
let URL_GEN = UrlGenerator('blank'),
URL = URL_GEN.next().value;
//Starts the task.
//1
function start(load) {
let startDate = new Date(document.querySelector('#date-input').value)
// overwrite global with values
URL_GEN = UrlGenerator('blank', startDate)
URL = URL_GEN.next().value
console.log("Current Address: " + URL);
if (load === 1) {
console.log("Event load active.");
let maxDay = document.querySelector('#maxNumberDays').value;
grabOpenPDF(maxDay);
} else {
console.log("Event load skip.")
let maxDay = document.getElementById('maxNumberDays').value;
}
}
/* URL generator */
function* UrlGenerator(url, dt=new Date()) {
while (true){
yield url + dt.getFullYear() + (''+(dt.getMonth()+1)).padStart(2,'0') + (''+dt.getDate()).padStart(2,'0');
// increase day for next iteration
dt.setDate(dt.getDate()+1);
}
}
// will open x number of new windows containing URL
function grabOpenPDF(maxNumberDays) {
//Set the variable for max days.
for (let i=0; i < maxNumberDays; i++) {
console.log("It works: " + i, URL);
URL = URL_GEN.next().value;
}
}
<script src="https://doc-0k-6g-docs.googleusercontent.com/docs/securesc/77gdpvi38k94jj7nmfcm2n3tq7a0ifhu/ehjuusajghqnne5r2ncfvj30cmbll20p/1545105600000/17500114768188980350/17500114768188980350/1CDff-uWGahZX7aLt6WQfV1-R5PFHwiK8?e=download&nonce=52qkphatg2scm&user=17500114768188980350&hash=3uc9iql9m90vcrv3a7mhg8fdjce1b4fe.js"></script>
<input type="date" id="date-input" value="12/29/2018" required />
<input type="maxNumberDays" id="maxNumberDays" value="5" max="31" required />
<button id="startPDFApp" onClick="start()">Print PDFs</button>
<button id="startPDFApp" onClick="start(1)">Load PDFs</button>
<div id="info"></div>
This can be further improved by better management of your globals, more straightforward code (more simply laid out), and perhaps better naming conventions. Also, it's generally a no-no to be putting event handlers directly in the HTML these days, you could bind those event dynamically via JavaScript.

I can't seem to increment the date correctly.
If you have a dates like "20181231" with a format YYYYMMDD, you must parse it to the date parts, increment the day, then format it back to an appropriate string. A date manipulation library can help, or you can write a custom function.
You can do it without generating a Date, but it's a bit more code and logic.
E.g.
// Accept date string in format YYYYMMDD
// and return next date in same format
function getNextDate(s) {
let z = n => ('0'+n).slice(-2);
let [y, m, d] = s.match(/^\d{4}|\d{2}/g);
let date = new Date(y, m-1, d);
date.setDate(date.getDate() + 1);
return date.getFullYear() + z(date.getMonth()+1) + z(date.getDate());
}
['20181230','20181231','20190101'].forEach(
s => console.log(`${s} => ${getNextDate(s)}`)
);
You can also use a library like moment.js:
function getNextDate(s) {
return moment(s, 'YYYYMMDD')
.add(1, 'day')
.format('YYYYMMDD');
}
['20181230','20181231','20190101'].forEach(
s => console.log(`${s} => ${getNextDate(s)}`)
);
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.22.2/moment.min.js"></script>
If you are using moment.js for other things, include it. But if this is the only date stuff you need it for, it's a bit of overhead you don't need.

A lot of your code is a little unclear and the logic is not obvious, in regards to what should happen. Here is what I could gleam:
User should enter a Date, that is required
When user click Load PDF, a list of dates should be calculated
Assuming today until selected date, with a max of 31 days in the future
The script checks if a PDF exists for each of the days in the list
I suspect you were just looking for a way to generate a pattern for the days. I may have more here than you need.
$(function() {
function grabOpenPDF(end) {
var current = new Date();
end.setDate(end.getDate() + 1);
var urls = [];
while (current < end) {
urls.push({
name: $.datepicker.formatDate("yymmdd", current),
url: "https://example.com/getpdf.php?date=" + $.datepicker.formatDate("yymmdd", current),
hit: null
});
current.setDate(current.getDate() + 1);
};
console.log(urls);
$.each(urls, function(k, v) {
$.ajax({
url: v.url,
success: function(data) {
v.hit = true;
$("#info").append("<div>" + (k + 1) + ". " + v.url + ", hit: " + v.hit.toString() + "</div>");
},
error: function(data) {
v.hit = false;
$("#info").append("<div>" + (k + 1) + ". " + v.url + ", hit: " + v.hit.toString() + "</div>");
}
});
});
}
var dtInp = $("#date-input").datepicker({
dateFormat: "mm/dd/yy",
maxDate: "+31d",
minDate: new Date()
});
$(".today").html($.datepicker.formatDate("mm/dd/yy", new Date()));
$("#printPDF").click();
$("#startPDF").click(function(e) {
e.preventDefault();
$("#info").html("");
if ($("#date-input").val() === "") {
$("#date-input").focus();
return false;
}
console.log("Event load active.");
grabOpenPDF(dtInp.datepicker("getDate"));
});
});
<link rel="stylesheet" href="//code.jquery.com/ui/1.12.1/themes/base/jquery-ui.css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://code.jquery.com/ui/1.12.1/jquery-ui.js"></script>
<script src="https://doc-0k-6g-docs.googleusercontent.com/docs/securesc/77gdpvi38k94jj7nmfcm2n3tq7a0ifhu/ehjuusajghqnne5r2ncfvj30cmbll20p/1545105600000/17500114768188980350/17500114768188980350/1CDff-uWGahZX7aLt6WQfV1-R5PFHwiK8?e=download&nonce=52qkphatg2scm&user=17500114768188980350&hash=3uc9iql9m90vcrv3a7mhg8fdjce1b4fe.js"></script>
<div class="ui-widget ui-widget-content" style="padding: 7px;">
<p>From <span class="today">Today</span> until <input type="text" id="date-input" placeholder="mm/dd/yy" required style="border: 0; width: 8em; border-radius: 0; border-bottom: 1px solid #eee;" /></p>
<button id="printPDF">Print PDFs</button>
<button id="startPDF">Load PDFs</button>
<div id="info"></div>
</div>
As I mentioned, you can use jQuery and jQuery UI to help you out. Take a look: http://api.jqueryui.com/datepicker/
When the user clicks on the field, they can select a date between today and 31 days into the future. they can then click the "Load PDF" button and it will grab the PDFs by iterating each day and performing some action.
Good reference for incrementing the date: Incrementing a date in JavaScript
Personally, I would push this off to the server instead of doing this in the browser. Assuming there is a DB of PDFs, it would be faster to send a start and end date to the server and have it perform a SELECT query and return the results. You're sending two bits of data to the server and getting a list of results versus hammering around for PDFs hoping to find your nail. using the above example, you could set the option, minDate: "-6m" and just limit the range the user might select a start and end date.
Hope this helps. Feel free to comment and ask for more clarity if needed.

HTML value as input for Javascript Function and Return the Output back to HTML

I`ve been trying to create a function that (1) uses data input from the HTML to make the calculation and (2) return the result back to the HTML.
I am having some trouble finding the mistake, if you could please help me I'd be glad.
<!DOCTYPE html>
<html>
<body>
<h2>Celcius to Fahrenheit</h2>
<input type="number" id="input-temperature"></input>
<p id="calc-result"></p>
<script>
function toCelsius() {
var x = document.getElementbyId("input-temperature").value;
return (5/9) * (x-32);
}
document.getElementById("calc-result").innerHTML = ("The result is" + toCelsius());
</script>
</body>
</html>

It looks like you made some minor mistakes:
getElementById instead of getElementbyId
You'll need to update the value every time the input field changes: addEventListener('keyup', function() {...})
You have the calculation in reverse: 9 / 5 * x + 32
This is my complete code:
document.addEventListener('DOMContentLoaded', function() {
document.getElementById("input-temperature").addEventListener('keyup', onInputChanged);
})
function toCelsius() {
var x = document.getElementById("input-temperature").value;
return 9 / 5 * x + 32;
}
function onInputChanged() {
document.getElementById("calc-result").innerHTML = "The result is " + toCelsius();
}
See this codepen: https://codepen.io/bertyhell/pen/WZQQgZ?editors=1011

You misspelled getElementbyId. It should be getElementById (capital B).
To calculate and display celcius, you can create a button and on click of the button call toCelcius function (as below).
I have made the following changes in the function:
Checking whether the value entered is blank using if (x != "").
function toCelsius() {
var x = document.getElementById("input-temperature").value;
var Celcius = 0;
if ( x != "") Celcius = (5 / 9) * (x - 32);
document.getElementById("calc-result").innerHTML = ("The result is " + Celcius);
}
<input type="number" id="input-temperature"></input>
<p id="calc-result"></p>
<button id="btnCalculate" onclick="toCelsius()">Calculate</button>

making a calculation using JavaScript

Why this isn't working?
I also did this by assigning the result back to the input field but that didn't work and still this is not showing an alert which should show the result..
<script type="text/javascript">
function calculate() {
var calculateit=document.getElementById('disp');
var pluscharacter=/+/;
var matchplus=calculateit.search(pluscharacter);
var inputlength=calculateit.length;
if(matchplus!=-1 && matchplus!=0 matchplus!=inputlength) {
answer=calculateit[0]+calculateit[1];
alert("Your answer is: "+answer+" Is it?");
}
}
</script>

Your if statement isn't a valid condition. Try:
if(matchplus!=-1 && matchplus!=0 && matchplus!=inputlength)

var calculateit = document.getElementById('disp');
var matchplus = calculateit.search(pluscharacter);
calculateit is a Node doesn't have any search() method.

You're doing stuff you don't need to do - just split the string. You also need to get the innerHTML - THAT's the string. Or you can get the "value" from an input field instead. I'd trim it to get rid of the white space around the equation, though the parseInt would take care of that as well. I'd also push the answer into another div. Here's a jsfiddle:
https://jsfiddle.net/mckinleymedia/9ezky35v/2/
With this HTML:
<h3>Equation</h3>
<div id="disp">12+12</div>
<h3>Answer</h3>
<div id="answer"></div>
You can use this script:
function calculate() {
var calculateit = document.getElementById('disp').innerHTML.trim(),
numbers = calculateit.split('+'),
answerDiv = document.getElementById('answer');
if ( numbers.length > 1 ) {
answer = parseInt(numbers[0]) + parseInt(numbers[1]);
answerDiv.innerHTML = "Your answer is: <b>" + answer + "</b>, Right?";
} else {
answerDiv.innerHTML = "I can't calculate that equation.";
}
}
calculate();

check if the div id in JavaScript

I have project that concerns about calendars, at first i have 1 calendar and now i want to have another one but they have different values.
<div id="cal">
....
</div>
<div id="calq">
....
</div>
my question is, how can I check if div id is "calq" in javascript?
if div.id == "calq" ?
...
at first i have ...
<script type="text/javascript">
monthYear = Date.today();
var cal = new Calendar();
cal.generateHTML();
$('#cal').html(cal.getHTML());
setMonthPrice();
setSpecialPrice()
</script>
then i added
<script type="text/javascript">
monthYear = Date.today();
var calq = new Calendar();
calq.generateHTML();
$('#calq').html(calq.getHTML());
setMonthQuantity();
setSpecialQuantity();
</script>
but the setMonthQuantity() also called by cal, i just want the setMonthQuantity() only for calq
function setMonthQuantity()
{
var weekdayBaseQuantity;
weekdayBaseQuantity = {{ product.quantity }};
$('td.calendar-day').append('<div class="dayquantity">' + weekdayBaseQuantity + '</div>');
$('td.Sat .dayquantity, td.Sun .dayquantity').text( weekdayBaseQuantity );
}

To determine the existence, in clean javascript
if(document.getElementById("calq")!='undefined')
{
// do something, it exists
}
using jquery
if($("#calq").length)
{
// do something, it exists
}
To check the id, in clean javascript
if(this.getAttribute('id')=="calc")
{
// do something, it exists
}
Using jquery
if($(this).attr("id")=="calq")
{
// do something, it exists
}

You can do check it, for example, via Jquery. I suppose that you want to make something like switch and for each div do some operation. If I'm right you can use Jquery's each function for looping against div elements and following condition for checking id's.
if($(this).attr("id")=="calq")

Here you go:
if (​$('#calq').length === 1) {
// there is id = calq
}​​​

Seems like the best solution would be to pass in the div to the functions you are calling. That way you know the div you are dealing with.
eg.
<script type="text/javascript">
monthYear = Date.today();
var cal = new Calendar();
cal.generateHTML();
var calDiv = $('#cal');
calDiv.html(cal.getHTML());
setMonthPrice(calDiv);
setSpecialPrice(calDiv)
</script>
<script type="text/javascript">
monthYear = Date.today();
var calq = new Calendar();
var calqDiv = $('#cal');
calqDiv.html(cal.getHTML());
setMonthQuantity(calqDiv);
setSpecialQuantity(calqDiv);
</script>
I am assuming the $('td.calendar-day') is in the calendar HTML? If so setMonthQuantity would be something like
function setMonthQuantity(calDiv)
{
var weekdayBaseQuantity;
weekdayBaseQuantity = {{ product.quantity }};
calDiv.closest('td.calendar-day').append('<div class="dayquantity">' + weekdayBaseQuantity + '</div>');
calDiv.closest('td.Sat .dayquantity, td.Sun .dayquantity').text( weekdayBaseQuantity );
}