JavaScript validation for empty input field
Greeting,
I have this input field
<input name="question"/> I want to call IsEmpty function when submit clicking submit button.
I tried the code below but did not work. any advice?!
<html>
<head>
<title></title>
<meta http-equiv="Content-Type" content="text/html; charset=unicode" />
<meta content="CoffeeCup HTML Editor (www.coffeecup.com)" name="generator" />
</head>
<body>
<script language="Javascript">
function IsEmpty() {
if (document.form.question.value == "") {
alert("empty");
}
return;
}
</script>
Question: <input name="question" /> <br/>
<input id="insert" onclick="IsEmpty();" type="submit" value="Add Question" />
</body>
</html>Answers:
See the working example here
You are missing the required <form> element. Here is how your code should be like:
function IsEmpty() {
if (document.forms['frm'].question.value === "") {
alert("empty");
return false;
}
return true;
}<form name="frm">
Question: <input name="question" /> <br />
<input id="insert" onclick="return IsEmpty();" type="submit" value="Add Question" />
</form>An input field can have whitespaces, we want to prevent that.
Use String.prototype.trim():
function isEmpty(str) {
return !str.trim().length;
}
Example:
const isEmpty = str => !str.trim().length;
document.getElementById("name").addEventListener("input", function() {
if( isEmpty(this.value) ) {
console.log( "NAME is invalid (Empty)" )
} else {
console.log( `NAME value is: ${this.value}` );
}
});<input id="name" type="text">Add an id "question" to your input element and then try this:
if( document.getElementById('question').value === '' ){
alert('empty');
}
The reason your current code doesn't work is because you don't have a FORM tag in there. Also, lookup using "name" is not recommended as its deprecated.
See @Paul Dixon's answer in this post : Is the 'name' attribute considered outdated for <a> anchor tags?
if(document.getElementById("question").value == "")
{
alert("empty")
}
Just add an ID tag to the input element... ie:
and check the value of the element in you javascript:
document.getElementById("question").value
Oh ya, get get firefox/firebug. It's the only way to do javascript.
My solution below is in es6 because I made use of const if you prefer es5 you can replace all const with var.
const str = " Hello World! ";
// const str = " ";
checkForWhiteSpaces(str);
function checkForWhiteSpaces(args) {
const trimmedString = args.trim().length;
console.log(checkStringLength(trimmedString))
return checkStringLength(trimmedString)
}
// If the browser doesn't support the trim function
// you can make use of the regular expression below
checkForWhiteSpaces2(str);
function checkForWhiteSpaces2(args) {
const trimmedString = args.replace(/^\s+|\s+$/gm, '').length;
console.log(checkStringLength(trimmedString))
return checkStringLength(trimmedString)
}
function checkStringLength(args) {
return args > 0 ? "not empty" : "empty string";
}Combining all the approaches we can do something like this:
const checkEmpty = document.querySelector('#checkIt');
checkEmpty.addEventListener('input', function () {
if (checkEmpty.value && // if exist AND
checkEmpty.value.length > 0 && // if value have one charecter at least
checkEmpty.value.trim().length > 0 // if value is not just spaces
)
{ console.log('value is: '+checkEmpty.value);}
else {console.log('No value');
}
});<input type="text" id="checkIt" required />Note that if you truly want to check values you should do that on the server, but this is out of the scope for this question.
<script type="text/javascript">
function validateForm() {
var a = document.forms["Form"]["answer_a"].value;
var b = document.forms["Form"]["answer_b"].value;
var c = document.forms["Form"]["answer_c"].value;
var d = document.forms["Form"]["answer_d"].value;
if (a == null || a == "", b == null || b == "", c == null || c == "", d == null || d == "") {
alert("Please Fill All Required Field");
return false;
}
}
</script>
<form method="post" name="Form" onsubmit="return validateForm()" action="">
<textarea cols="30" rows="2" name="answer_a" id="a"></textarea>
<textarea cols="30" rows="2" name="answer_b" id="b"></textarea>
<textarea cols="30" rows="2" name="answer_c" id="c"></textarea>
<textarea cols="30" rows="2" name="answer_d" id="d"></textarea>
</form>I would like to add required attribute in case user disabled javascript:
<input type="text" id="textbox" required/>
It works on all modern browsers.
if(document.getElementById("question").value.length == 0)
{
alert("empty")
}
<pre>
<form name="myform" action="saveNew" method="post" enctype="multipart/form-data">
<input type="text" id="name" name="name" />
<input type="submit"/>
</form>
</pre>
<script language="JavaScript" type="text/javascript">
var frmvalidator = new Validator("myform");
frmvalidator.EnableFocusOnError(false);
frmvalidator.EnableMsgsTogether();
frmvalidator.addValidation("name", "req", "Plese Enter Name");
</script>before using above code you have to add the gen_validatorv31.js file
You can loop through each input after submiting and check if it's empty
let form = document.getElementById('yourform');
form.addEventListener("submit", function(e){ // event into anonymous function
let ver = true;
e.preventDefault(); //Prevent submit event from refreshing the page
e.target.forEach(input => { // input is just a variable name, e.target is the form element
if(input.length < 1){ // here you're looping through each input of the form and checking its length
ver = false;
}
});
if(!ver){
return false;
}else{
//continue what you were doing :)
}
})
<script type="text/javascript">
function validateForm() {
var a = document.forms["Form"]["answer_a"].value;
var b = document.forms["Form"]["answer_b"].value;
var c = document.forms["Form"]["answer_c"].value;
var d = document.forms["Form"]["answer_d"].value;
if (a == null || a == "", b == null || b == "", c == null || c == "", d == null || d == "") {
alert("Please Fill All Required Field");
return false;
}
}
</script>
<form method="post" name="Form" onsubmit="return validateForm()" action="">
<textarea cols="30" rows="2" name="answer_a" id="a"></textarea>
<textarea cols="30" rows="2" name="answer_b" id="b"></textarea>
<textarea cols="30" rows="2" name="answer_c" id="c"></textarea>
<textarea cols="30" rows="2" name="answer_d" id="d"></textarea>
</form>