How to check empty/undefined/null string in JavaScript?

If we want to check any string either it is filled or empty we can use Javascript for such purpose for example : form validation. 

Example :

html

<script>
    function checkempty(form) {
        if (form.name.value == null ||
            form.name.value == undefined ||
            form.name.value.length == 0) {

            alert("Name cannot be empty\n");
            return false;
        } else {
            alert("Your response has been recorded\n");
            return true;
        }
    }
</script>
<form onsubmit="return checkempty(form1)" action="#" method="post" name="form1">
    <label>Enter your name</label>
    <br>
    <input type="string" placeholder="Enter name" name="name" />
    <br>
    <br>
    <label>Enter Email</label>
    <br>
    <input type="" placeholder="Enter email" name="email" />
    <br>
    <br>
    <label>Enter password</label>
    <br>
    <input type="password" placeholder="Enter password " name="password1" />
    <br>
    <br>
    <label>Confirm password</label>
    <br>
    <input type="password" placeholder="Enter password " name="password2" />
    <br>
    <br>
    <input type="submit" value="submit" />
    <br>
</form>

Output: If the name is empty.

How to check empty/undefined/null string in JavaScript?

Simplified with 3 Different Methods

Method 1: Using === operator

Using === operator we will check the string is empty or not. If empty then it will return “Empty String” and if the string is not empty it will return “Not Empty String”

Javascript

// function to check string is empty or not
function checking(str){
// checking the string using === operator
    if (str === "") {
        console.log("Empty String")
    }
    else {
       console.log("Not Empty String")
    }
}

// calling the checking function with empty string
checking("")
// calling the checking function with not an empty string
checking("GeeksforGeeks")

Output:

Empty String
Not Empty String

Method 2: By using the length and ! operator

This function will check the length of the string also by using ! operator we will check string is empty or not.

Javascript

// function to check string is empty or not
function checking(str) {
    // checking the string using ! operator and length
    // will return true if empty string and false if string is not empty
    return (!str || str.length === 0 );
}
// calling the checking function with empty string
console.log(checking(""))
// calling the checking function with not an empty string
console.log(checking("GeeksforGeeks"))

Output:

true
false

Method 3: By using replace

It will ensure that the string is not just a group of empty spaces where we are doing replacement on the spaces.

Javascript

// function to check string is empty or not
function checking(str){
    if(str.replace(/\s/g,"") == ""){
        console.log("Empty String")
    }
    else{
        console.log("Not Empty String")
    }
}

// calling the checking function with empty string
checking("  ")
// calling the checking function with not an empty string
checking("Hello Javascript")

Output:

Empty String
Not Empty String