javascript check if field is empty – Checking if an input is empty with JavaScript – Use the === Operator to Check if the String Is Empty, Use the length Property to Check if the String Is Empty and Convert the Variable to Boolean to Check if the String Is Empty in JavaScript.
Use the === Operator to Check if the String Is Empty in JavaScript
console.log(false === "")
console.log(undefined === "")
console.log(2 === "")
console.log(null === "")
console.log("Welcome Pakainfo!" === "")
console.log("" === "")
In JavaScript, you can check if a value is empty using several different methods, depending on the type of value you’re dealing with:
const myString = "";
if (myString === "") {
// the string is empty
}
let myVariable = null; // or let myVariable;
if (myVariable === null || myVariable === undefined) {
// the value is null or undefined
}
const myArray = [];
if (myArray.length === 0) {
// the array is empty
}
const myObject = {};
if (Object.keys(myObject).length === 0) {
// the object is empty
}
Note that if you’re working with a string, you may also want to trim it before checking if it’s empty to ensure that any leading or trailing whitespace is removed:
const myString = " ";
if (myString.trim() === "") {
// the string is empty
}
It’s also worth noting that in JavaScript, an empty value, such as an empty string or null, is considered falsy, while a non-empty value is considered truthy. Therefore, you can also check for an empty value using an if statement with the double negation operator, which coerces the value to a boolean and returns its opposite:
const myString = "";
if (!!myString) {
// the string is not empty
} else {
// the string is empty
}
Check for an Empty String in JavaScript
const input = document.querySelector('input')
input.addEventListener('input', evt => {
// Validate input
})
Example:
var userStr = ""
var memverStr = 0
var clientStr = false
console.log(userStr == "")
console.log(memverStr == "")
console.log(clientStr == "")
if(document.getElementById("interview_no").value.length == 0)
{
alert("empty")
}
Use the length Property to Check if the String Is Empty in JavaScript
let userStr = "Welcome Pakainfo!";
let memverStr = "";
let clientStr = 4;
console.log(userStr.length === 0)
console.log(memverStr.length === 0)
console.log(clientStr.length === 0)
const inputFeilds = document.querySelectorAll("input");
const validInputs = Array.from(inputFeilds).filter( input => input.value !== "");
console.log(validInputs) //[array with valid inputs]
Convert the Variable to Boolean to Check if the String Is Empty in JavaScript
let userStr = "Welcome Pakainfo!";
let memverStr = "";
console.log(!!userStr)
console.log(!!memverStr)
console.log(Boolean(userStr))
console.log(Boolean(memverStr))
index.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initialscale=1.0">
<title>Check if value is empty in JavaScript - www.pakainfo.com </title>
<link rel="stylesheet" href="//code.jquery.com/ui/1.12.1/themes/base/jquery-ui.css">
<script src="https://code.jquery.com/jquery-1.12.4.js"></script>
<script src="https://code.jquery.com/ui/1.12.1/jquery-ui.js"></script>
</head>
<body>
<form name="signup" onsubmit="return prodfileNameMember()">
memberNAME: <input type="text" name="membername">
<input type="submit" value="Save">
</form>
<script>
function prodfileNameMember() {
var membername = document.forms["signup"]["membername"].value;
if (membername == null || membername == "") {
alert("Please enter> the membername. Can’t be blank or empty !!!");
return false;
}
}
</script>
</body>
</html>
I hope you get an idea about javascript check if field is empty.