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How do I find out if a input element's value is blank (null)

I have following code to check if the inputs with the ids emailForm and nameForm are blank, this however isn't working when I test the form by leaving it blank.
function setInfo() {
if (document.getElementById("emailForm").value == null ||
document.getElementById("nameForm").value == null) {
alert("Please Fill in all sections");
} else {
email = document.getElementById("emailForm").value;
name = document.getElementById("nameForm").value;
loaded();
}
}
Could someone help me with this, thanks!

Instead of checking for null specifically, you should check for falsy values. In some cases, the values for empty textboxes will be an empty string.
Replace this:
if (document.getElementById("emailForm").value == null || document.getElementById("nameForm").value == null) {
with this:
if (!document.getElementById("emailForm").value || !document.getElementById("nameForm").value) {

You shouldn't be checking whether the fields are null, you should be checking whether they content is an empty string (with .value == '').
This can be seen working in the following:
function setInfo() {
if (document.getElementById("emailForm").value == '' ||
document.getElementById("nameForm").value == '') {
console.log("Please fill in all sections");
} else {
email = document.getElementById("emailForm").value;
name = document.getElementById("nameForm").value;
//loaded();
console.log("All sections filled in");
}
}
const button = document.getElementById('go');
button.addEventListener('click', function() {
setInfo();
});
<input id="emailForm" />
<input id="nameForm" />
<button id="go">Go</button>

Make sure you calling function setInfo()
function setInfo() {
// You can check Value.Length also or
if (document.getElementById("emailForm").value === "" ||
document.getElementById("nameForm").value === "") {
alert("Please Fill in all sections");
} else {
email = document.getElementById("emailForm").value;
name = document.getElementById("nameForm").value;
loaded();
}
}

Try below solution:
function setInfo() {
var email=document.getElementById("emailForm").value;
var name=document.getElementById("nameForm").value;
if (email=='' || email==null || name=='' || name== null ) { // OR if (!email || !name)
alert("Please Fill in all sections");
return;
} else {
loaded();
}
}

You should check whether the string is empty or not instead of null. Try using the code below:
function setInfo() {
var a=document.getElementById("emailForm").value;
var b=document.getElementById("nameForm").value;
if (a == "" ||
b == "") {
alert("Please Fill in all sections");
} else {
email =
document.getElementById("emailForm").value;
name =
document.getElementById("nameForm").value;
alert("success alert");
}
}

How do I use javascript to prevent form submission because of empty fields?

How do I make a script in javascript to output an error and prevent form submission with empty fields in the form? Say the form name is "form" and the input name is "name". I have been having some trouble with PHP not always handling the empty fields correctly, so I would like this as a backup. Any help is appreciated, thanks.

HTML Code :-
<form name='form'>
<input type="button" onclick="runMyFunction()" value="Submit form">
</form>
Javascript Code :-
function runMyFunction()
{
if (document.getElementsByName("name")[0].value == "")
{
alert("Please enter value");
}
else
{
var form= document.getElementsByName("form")[0];
form.submit();
}
}

Claudio's answer is great. Here's a plain js option for you. Just says to do nothing if field is empty - and to submit if not.
If you need to validate more than one, just add an && operator in the if statement and add the same syntax for OtherFieldName
function checkForm(form1)
{
if (form1.elements['FieldName'].value == "")
{
alert("You didn't fill out FieldName - please do so before submitting");
return false;
}
else
{
form1.submit();
return false;
}
}

This is untested code but it demonstrates my method.
It will check any text field in 'form' for empty values, and cancel the submit action if there are any.
Of course, you will still have to check for empty fields in PHP for security reasons, but this should reduce the overhead of querying your server with empty fields.
window.onload = function (event) {
var form = document.getElementsByName('form')[0];
form.addEventListener('submit', function (event) {
var inputs = form.getElementsByTagName('input'), input, i;
for (i = 0; i < inputs.length; i += 1) {
input = inputs[i];
if (input.type === 'text' && input.value.trim() === '') {
event.preventDefault();
alert('You have empty fields remaining.');
return false;
}
}
}, false);
};

Attach an event handler to the submit event, check if a value is set (DEMO).
var form = document.getElementById('test');
if (!form.addEventListener) {
form.attachEvent("onsubmit", checkForm); //IE8 and below
}
else {
form.addEventListener("submit", checkForm, false);
}
function checkForm(e) {
if(form.elements['name'].value == "") {
e.preventDefault();
alert("Invalid name!");
}
}

Check if placeholder text already exists within a string

I have an #error paragraph. Everytime there is an error within the form on submit. The inputs placeholder text gets added to the #error paragraph.
My problem:
It happens everytime a user clicks submit. So the #error message returns:
Please fill in yourfirst name, last name, company, position, first
name, last name, company, position, first name, last name, company,
position, first name, last name, company, position, first name, last
name, company, position, first name, last name, company, position,
I've looked for other solutions and tried this:
if (input.attr('placeholder').indexOf($('#error')) >= 0){
} else{
$('#error').append(input.attr('placeholder').toLowerCase() + ', ');
}
Is there any way to check if the placeholder text already exists in the #error message? Here's a fiddle. I'm sorry it's so convoluted. But its what i've been working on and had it handy.
Thanks for your help in advance!

http://jsfiddle.net/8YgNT/20/
var errorText = '';
//Validate required fields
for (i = 0; i < required.length; i++) {
var input = $('#' + required[i]);
if ((input.val() == "") || (input.val() == emptyerror)) {
input.addClass("tobefixed");
errornotice.fadeIn(750);
if (input.attr('placeholder').indexOf($('#error')) >= 0) {
// do nothing
} else {
errorText = errorText + $(input).attr('placeholder').toLowerCase() + ', ';
}
input.val(emptyerror);
errornotice.fadeIn(750);
} else {
input.removeClass("tobefixed");
}
}
$('#error').html('').append('Please fill in your ' + errorText);

I simple add one line in your fiddle and it's working now:
required = ["id_first_name", "id_last_name", "id_firmbox", "id_job_title"];
errornotice = $("#error");
emptyerror = "Please fill out this field.";
$("#startform").submit(function(){
//Validate required fields
$("#error").html("Please fill in your");
for (i=0;i<required.length;i++) {
var input = $('#'+required[i]);
if ((input.val() == "") || (input.val() == emptyerror)) {
input.addClass("tobefixed");
errornotice.fadeIn(750);
// =====Here===== //
if (input.attr('placeholder').indexOf($('#error')) >= 0){
} else{
$('#error').append(input.attr('placeholder').toLowerCase() + ', ');
}
// ============== //
input.val(emptyerror);
errornotice.fadeIn(750);
} else {
input.removeClass("tobefixed");
}
}
if ($(":input").hasClass("tobefixed")) {
return false;
} else {
errornotice.hide();
return true;
}
});
$(":input").focus(function(){
if ($(this).hasClass("tobefixed") ) {
$(this).val("");
$(this).removeClass("tobefixed");
}
});
This line do the all trick:
$("#error").html("Please fill in your");
Saludos ;)

If you want to check whether #error contains the string you're wondering about, you can use
($('#error').text().indexOf(a_string)) != -1
This will return true if #error contains a_string.
There's a longer discussion on searching strings for other strings in this question.

It seems you're doing it the wrong way round (and forgetting to get the text out of the #error element):
if ( $('#error').text().indexOf( input.attr('placeholder') ) >= 0)

Remaking jQuery form validation

I am trying to remake a jQuery script by (http://jorenrapini.com/blog/javascript/the-simple-quick-and-small-jquery-html-form-validation-solution). This script is checking if a from is filled, if not a error message will appear.
What I want to do is to only get the error message when one of two form input-fields are filled out, if none of them are then they should be ignored. The form fields are named "firstinput" and "secondinput" (you can see their id in the code).
$(document).ready(function(){
// Place ID's of all required fields here.
required = ["firstinput", "secondinput"];
// If using an ID other than #email or #error then replace it here
email = $("#email");
errornotice = $("#error");
// The text to show up within a field when it is incorrect
emptyerror = "Please fill out this field.";
emailerror = "Please enter a valid e-mail.";
$("#theform").submit(function(){
//Validate required fields
for (i=0;i<required.length;i++) {
var input = $('#'+required[i]);
if ((input.val() == "") || (input.val() == emptyerror)) {
input.addClass("needsfilled");
input.val(emptyerror);
errornotice.fadeIn(750);
} else {
input.removeClass("needsfilled");
}
}
// Validate the e-mail.
if (!/^([a-zA-Z0-9_\.\-])+\#(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/.test(email.val())) {
email.addClass("needsfilled");
email.val(emailerror);
}
//if any inputs on the page have the class 'needsfilled' the form will not submit
if ($(":input").hasClass("needsfilled")) {
return false;
} else {
errornotice.hide();
return true;
}
});
// Clears any fields in the form when the user clicks on them
$(":input").focus(function(){
if ($(this).hasClass("needsfilled") ) {
$(this).val("");
$(this).removeClass("needsfilled");
}
});
});
Can anybody please help me with a solution, I would really appreciate it.
/A girl that spend a LOT of time solving this without luck :(

I would wrap your for loop in a conditional that evaluates if one or the other has a value.
if($("#field1").val() == "" && $("#field2").val() == ""){
//Ignore
}else{
//Do something
}
$(document).ready(function(){
// Place ID's of all required fields here.
required = ["firstinput", "secondinput"];
// If using an ID other than #email or #error then replace it here
email = $("#email");
errornotice = $("#error");
// The text to show up within a field when it is incorrect
emptyerror = "Please fill out this field.";
emailerror = "Please enter a valid e-mail.";
$("#theform").submit(function(){
//Validate required fields
if($("#firstinput").val() != "" || $("#secondinput").val() != "")
{
for (i=0;i<required.length;i++) {
var input = $('#'+required[i]);
if ((input.val() == "") || (input.val() == emptyerror)) {
input.addClass("needsfilled");
input.val(emptyerror);
errornotice.fadeIn(750);
} else {
input.removeClass("needsfilled");
}
}
}
// Validate the e-mail.
if (!/^([a-zA-Z0-9_\.\-])+\#(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/.test(email.val())) {
email.addClass("needsfilled");
email.val(emailerror);
}
//if any inputs on the page have the class 'needsfilled' the form will not submit
if ($(":input").hasClass("needsfilled")) {
return false;
} else {
errornotice.hide();
return true;
}
});
// Clears any fields in the form when the user clicks on them
$(":input").focus(function(){
if ($(this).hasClass("needsfilled") ) {
$(this).val("");
$(this).removeClass("needsfilled");
}
});
});

how do i put the following in a for loop

I would like to put the following in a for loop but i am having difficulties. Any help would be appreciated
$("input:submit").click(function(){
if (!$("input[name=attendance1]").is(":checked")) {
alert('Please select preference');
return false;
}
else if (!$("input[name=attendance2]").is(":checked")) {
alert('Please select preference');
return false;
}
else if (!$("input[name=attendance3]").is(":checked")) {
alert('Please select preference');
return false;
}
});
});
I have tried:
for($i=1; $i<=3; $i++)
{
$("input:submit").click(function(){
if (!$("#food" + $i).is(":checked")) {
alert('Please select preference');
return false;
}
});
});

First fix:
alert('Please select preference);
with
alert('Please select preference');
Then if you want to loop:
for (var i = 0; i < 3; i++) {
if (!$("input[name=attendance" + i + "]").is(":checked")) {
alert('Please select preference');
return false;
}
}
Or better yet use jQuery's startsWith selector:
if (!$('input[name^="attendance"]').is(":checked")) {
alert('Please select preference');
return false;
}
Example

You're missing a closing single quotation mark on all 3 alert statements.

I generally use a class name on my DOM elements when I want to do something like this. That makes it easier to iterate through the elements using .each(). I was not aware of the startsWith selector mentioned above, but it does look a bit cleaner than my method.
<!-- DO STUFF -->
<input name="attendance1" class="my-unique-class-name" />
<input name="attendance2" class="my-unique-class-name" />
<input name="attendance3" class="my-unique-class-name" />
<!-- DO STUFF -->
<script type="text/javascript">
$("input:submit").click(function(){
var valid = true;
$("input.my-unique-class-name").each(function (el) {
if ( ! $(el).is(":checked") ) {
valid = false;
}
});
if ( ! valid ) {
alert('Please select preference');
return false;
}
});
</script>

Here's my take on it. it has the advantage of you listing down in an array what names you want checked, regardless what names they are
//jQuery '.on()' for versions 1.7+
$("input:submit").on('click', function() {
//assume valid unless found otherwise
var valid = true;
//add the input names you want to verify
var nameList = [
'attendance1',
'attendance2',
'attendance3'
];
//loop through names
for (var i = 0; i < nameList.length; i++) {
var checked = $('input[name="'+nameList[i]+'"]').is(':checked');
if (!checked) {
alert('Please select a preference');
//mark false when something wrong found
valid = false;
}
}
//check if validity persisted
if(valid){
//do something
}
//prevent default actions
return false;
});​