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Connect script inside form tag (locally) [duplicate]

I wanna write my own form validation javascript library and I've been looking on google how to detect if a submit button is clicked but all I found is code where you have to use onClick on onSubmit="function()" in html.
I would like to make this javascript so that I don't have to touch any html code like adding onSubmit or onClick javascript.

Why do people always use jQuery when it isn't necessary?
Why can't people just use simple JavaScript?
var ele = /*Your Form Element*/;
if(ele.addEventListener){
ele.addEventListener("submit", callback, false); //Modern browsers
}else if(ele.attachEvent){
ele.attachEvent('onsubmit', callback); //Old IE
}
callback is a function that you want to call when the form is being submitted.
About EventTarget.addEventListener, check out this documentation on MDN.
To cancel the native submit event (prevent the form from being submitted), use .preventDefault() in your callback function,
document.querySelector("#myForm").addEventListener("submit", function(e){
if(!isValid){
e.preventDefault(); //stop form from submitting
}
});
Listening to the submit event with libraries
If for some reason that you've decided a library is necessary (you're already using one or you don't want to deal with cross-browser issues), here's a list of ways to listen to the submit event in common libraries:
jQuery
$(ele).submit(callback);
Where ele is the form element reference, and callback being the callback function reference. Reference
<iframe width="100%" height="100%" src="http://jsfiddle.net/DerekL/wnbo1hq0/show" frameborder="0"></iframe>
AngularJS (1.x)
<form ng-submit="callback()">
$scope.callback = function(){ /*...*/ };
Very straightforward, where $scope is the scope provided by the framework inside your controller. Reference
React
<form onSubmit={this.handleSubmit}>
class YourComponent extends Component {
// stuff
handleSubmit(event) {
// do whatever you need here
// if you need to stop the submit event and
// perform/dispatch your own actions
event.preventDefault();
}
// more stuff
}
Simply pass in a handler to the onSubmit prop. Reference
Other frameworks/libraries
Refer to the documentation of your framework.
Validation
You can always do your validation in JavaScript, but with HTML5 we also have native validation.
<!-- Must be a 5 digit number -->
<input type="number" required pattern="\d{5}">
You don't even need any JavaScript! Whenever native validation is not supported, you can fallback to a JavaScript validator.
Demo: http://jsfiddle.net/DerekL/L23wmo1L/

This is the simplest way you can have your own javascript function be called when an onSubmit occurs.
HTML
<form>
<input type="text" name="name">
<input type="submit" name="submit">
</form>
JavaScript
window.onload = function() {
var form = document.querySelector("form");
form.onsubmit = submitted.bind(form);
}
function submitted(event) {
event.preventDefault();
}

Based on your requirements you can also do the following without libraries like jQuery:
Add this to your head:
window.onload = function () {
document.getElementById("frmSubmit").onsubmit = function onSubmit(form) {
var isValid = true;
//validate your elems here
isValid = false;
if (!isValid) {
alert("Please check your fields!");
return false;
}
else {
//you are good to go
return true;
}
}
}
And your form may still look something like:
<form id="frmSubmit" action="/Submit">
<input type="submit" value="Submit" />
</form>

If you have multiple forms in same page & you wants to handle submit event Listener without using Id
jQuery
$('form').submit(function (event) {
targetObj = event.target;
// do your logic
});
Pure JavaScript trick
Onload just do below way.
for(var i=0; i<document.forms.length; i++){
var form = document.forms[i];
form.addEventListener("submit", myListener,false);
}
credit :- Multiple Form Submit Event Listener Handling using JavaScript credit goes to Jan Pfeifer's Answer on StackOverflow Community
I hope this helps to someone

With jQuery:
$('form').submit(function () {
// Validate here
if (pass)
return true;
else
return false;
});

Why doesn't my statement to disable form submission work?

I have a checkout form on my website that uses a custom validation method implemented with Bootstrap. It has a JavaScript function to prevent the form from being submitted multiple times if it is filled out correctly. I'm using a technique commonly suggested on SO to disable the submission, albeit with vanilla JavaScript instead of JQuery. This is the function:
function submitForm() {
// Fetch all the forms we want to apply custom Bootstrap validation styles to
var forms = document.getElementsByClassName('needs-validation');
// Loop over them and prevent submission
var validation = Array.prototype.filter.call(forms, function(thisForm) {
event.preventDefault();
if (thisForm.checkValidity() === false) {
event.stopPropagation();
}
thisForm.classList.add('was-validated');
<?php if(isset($shipping)){
echo "stripe.createToken(card).then(function(result) {
if (result.error) {
// Inform the user if there was an error
} else {
thisForm.addEventListener('submit', function(event){
event.preventDefault();
return false;
});
// Send the token to the server
console.log('Sending token ' + result.token + '.');
}
});";
}?>
});
};
The form is created like this:
<form id="payment-form" onsubmit="return submitForm()" class="needs-validation" novalidate>
When I test the page with the form filled out correctly, double clicking the submit button prints the "Sending token" message to the console twice when it should only happen once. I thought maybe it was because it was taking too long to get to the part of the function where the form is disabled, but the message prints again no matter how many times the button is clicked.

Using inline event handlers is bad practice and results in poorly factored, hard-to-manage code. Seriously consider attaching your events with JavaScript, instead, eg: https://developer.mozilla.org/en/DOM/element.addEventListener
You're not calling the validation function with the event of when the form was clicked - and then you reference event.preventDefault();, but event is not defined.
Try something like this instead. Remove the onsubmit attribute, and do:
[...document.querySelectorAll('.needs-validation')].forEach((thisForm) => {
thisForm.addEventListener('submit', (event) => { // add the event argument here
event.preventDefault();
if (thisForm.checkValidity() === false) {
// rest of your code
(though, I don't see why you're using .filter in the first place it doesn't make sense here - did you mean to use forEach? And if there's only one #payment-form, couldn't you have selected that by itself?)

To stop a form from submitting you should call event.preventDefault() or return false;
<form onsubmit="handleSubmit"></form>
handlesubmit(event) {
event.preventDefault();
// or return false;
}

How to prevent submitting form based on text in an html element?

I have a form in that I have User Id availability check. So if Id is already in DB it will show a message "Id is already in use". In that case I have to avoid submitting the form. For that my html is as follow,
<div>
<label><strong>Teacher Id:</strong></label>
<input type="text" name="teacherId" id="teacherId" placeholder="Enter Teacher Id" >
</div><span class="status" id="status"></span>
Here span will have the text about availability,
The value to span comes form jquery post call,
$.post('<%=request.getContextPath()%>/controller/TeacherIdCheckController',
{'teacherId':teacherId},
function(data)
{
$('.status').html(data);
});
}
This works fine, to prevent submitting I wrote javascript function as,
function checkTeacherId(){
alert(" in checkTecherId()");
var status=$("#status").text();
alert(status);
if(status=="Id in use try another")
preventDefault();
else
return true;
}
Everything works fine but this javascript function is not working fine so I cant able to prevent submit in case of Id already exist in DB. So please anyone help me in this.

Just because you need to pass the event in the function's arg:
function checkTeacherId(e){ // <---pass the event here
.....
if(status=="Id in use try another")
e.preventDefault(); // and stop it here using dot notation
else
return true;
}
As per your comment you can pass the event to your function in your onclick handler:
onclick="checkTeacherId(event);"
Fiddle
Okay! As #Sanjeev tried commenting on best approach for this work then as you are using jQuery then you can just do this as per best approach like Unobrusive Javascript (removing this inliner scripts just like above posted):
function checkTeacherId(e){ // <---pass the event here
.....
if(status=="Id in use try another")
e.preventDefault(); // and stop it here using dot notation
else
return true;
}
$(function(){
$('#yourformid').on('submit', function(e){
checkTeacherId(e);
});
});
Use this approach if you want to externalize your scripts as declare the function in global scope and put your event handler in doc ready with submit event.
Updated fiddle with unobtrusive way.

Solution as per best practice for form validation:
You have implemented form submit via Submit button and not through js like document.getElementById("myForm").submit();
I don't see any point in using onclick handler on submit button for validation, use the native onsubmit Event Attribute, else you will keep on breaking submit flow.
onsubmit is made for validating form and stopping form submission if validation fails.
This will work sure shot in all browsers and is the correct approach for form validation
Example:
<form action="demo_form.asp" onsubmit="return checkTeacherId()">
function checkTeacherId(){
var status=$("#status").text();
if(status==="Id in use try another"){
return false
}
else{
return true;
}
}

Calling Javascript on a form post to update UI via jQuery

I have an Input element that submits a form:
<input type="submit" value="Download" id="downloadButton" class="btn-download" />
I need the button to call a javascript function, and then post the form normally.
How would that be done in jQuery?

$('#downloadButton').on('click', function (e) {
e.preventDefault();
//call your function here
$(this).parents('form').submit();
});
the preventDefault() call is important because it stops the submission of the form so you can call your function before the form submit is called at the end.

You can do:
<form onsubmit="return doSomething();">
</form>
function doSomething() {
// do something
return true;
}
If in the doSomething function you don't like what you're seeing, then return false instead of true.
EDIT
The jQuery equivalent (to satisfy both commenters): remove the onsubmit from the HTML and replace with:
jQuery(document).ready(function () {
jQuery("form#myFormId").submit(doSomething);
});

Take a look at this jsfiddle
It changes the case of textbox content to to upper case before submitting the form
$('#formID').on('submit', function () {
//var form = $(this),
//input = form.find('input[type="text"]');
//input.val(input.val().toUpperCase());
//alert(input.val());
// call your function here!
});

this is what you request:
1.- click a button (adding event handler)
2.- call a function
3.- submit form
myfunction(){
//do wathever you want
$('#formid').submit();
}
$(document).on("click", "#downloadButton", myfunction);
you can do also:
$(document).on("click", "#downloadButton", function(event){
$('#formid').submit();
});
without having an extra function
but the solution of #Paritosh is the more accurate.

jsFiddle here
Change input type to type="button" and use:
$('#downloadButton').click(function() {
//Do any javascript stuff here
//And here, etc. Then, when ready...
$('#yourFormID').submit();
});
I recommend assigning an ID attribute to your form as it is good practice.
<form id="yourFormID" action="" method="POST">
Perhaps you have only one form on this page, in that case $('form').submit() is fine. But in future (or perhaps even on this page, you haven't said) you may have multiple forms on a page and therefore the ID is necessary to specify the exact form to be submitted.
Note that if you do NOT change the submit button element's <input type="submit" to <input type="button", then you must use e.preventDefault() to prevent the button's default action. Why bother with that? Just change type="button" and use less code and less future confusion.

add a submit event on form.
$('form').submit(function(event){
event.preventDefault();
var formObj = $(this);
var formData = formObj.serialize();
$.ajax({
type: 'post',
data: formData
}).done(function(response){
console.info(response);
// update UI here accordingly.
});
});

Where to add onsubmit to a form in Javascript

In my HTML I've got a form without an onsubmit event listener:
<form action="contact.php" method="post" id="contact">
...
<input type="submit" value="Send" />
</form>
As a result, the form is always posted whenever I click the "Send" button. However, I'd like to validate the input first, so I'd like to attach an event listener and intercept the post. This is how I attach the event listener to the form:
window.onload = function() {
function validate() {
return window.confirm("Confirm");
}
var form = document.getElementById("contact");
form.addEventListener("submit", validate);
}
While the event listener is being executed, if I go by above approach the form is always posted! However, if I make the validate() function global and use onsubmit="return validate();" in the <form> tag, then the form is only being submitted conditionally, as expected.
Why does this not work by adding the validate() function as above? It seems the false return value gets lost?

Modern event handling has a more complex API, it gives more flexibility but that comes at the cost of not being able to tie behaviour to a simple boolean result.
For your use case, you need to capture the event object:
function validate(ev) {
Then you can prevent the default action on it:
if (!confirm('Confirm')) {
ev.preventDefault();
}