Javascript if variable is empty

How to Check if Variable is Empty or Undefined in Javascript

In this tutorial, you will learn how to check if variable is empty or undefined in javascript. Whenever you create a variable and do not assign any value to it, by default it is always undefined. It becomes defined only when you assign some value to it. A variable is considered to be empty when it holds an empty string as its value. An empty string has a length of 0.

There are numerous ways to check if a variable is empty or undefined. We are going to use one of the easiest solutions which involve the usage of the typeof and ternary ( ? ) operators. The typeof operator returns the type of the variable. The ternary operator is also known as the conditional operator which acts similar to the if-else statement.

In the following example, we have one global variable and upon click of a button, we will check if the variable is empty or undefined and display the result on the screen. Please have a look over the code example and the steps given below.

• We have 3 elements in the HTML file ( div , button , and h1 ). The div element is just a wrapper for the rest of the elements.
• The innerText for the button element is “Check” and for the h1 element, it is “Result” .
• We have done some basic styling using CSS and added the link to our style.css stylesheet inside the head element.
• We have also included our javascript file script.js with a script tag at the bottom.

• We have selected the button element and h1 element using the document.querySelector() method and stored them in btnCheck and result variables respectively.
• We have a global variable myVar which holds a string as its value.
• We have attached a click event listener to the button element.
• In the event handler function, we are calling checkVariable() method and passing it myVar as a parameter. This method will verify whether myVar is empty or undefined.
• In the checkVariable() method, we are using typeof and ternary ( ? ) operators as well as switch statement for verification. Depending upon the result of the check, this method will return “Empty” , «Undefined» or “Neither Empty nor Undefined” .
• We are displaying the returned value in the h1 element using the innerText property.

let btnCheck = document.querySelector("button"); let result = document.querySelector("h1"); let myVar = ''; btnCheck.addEventListener("click", () => < result.innerText = checkVariable(myVar); >); function checkVariable(value) < let output = typeof value == "undefined" ? 1 : 0; if (output == 0) output = value == '' ? 2 : 0; switch (output) < case 1: return "Undefined"; case 2: return "Empty"; default: return "Neither Empty nor Undefined"; >>

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How to Check if a Variable is Null or Empty in JavaScript

In JavaScript, or any other language, when you create a variable, you assign it some values. However, in the other case, it acts like an undefined variable. If a variable holds an empty string, it means the variable is “empty” due to its zero length. In order to indicate the absence of any object value, you can also give a variable the value “null“.

This blog will discuss the methods for determining whether a variable is null or empty.

How to Check if a Variable is Null or Empty in JavaScript?

For verifying whether the variable is null or empty, you can use the following methods:

Let’s go through the working of these methods individually.

Method 1: Check if a Variable is Null or Empty Using length Property

To verify whether a variable is null or empty, you can use the “length” property, which is the fundamental property of JavaScript. It is possible to perform self-reflection in JavaScript functions that interact with other functions by using the length property

Syntax
Follow the below-given syntax for the length property:

Here, we will check if the length of the variable “val” is zero or not.

Example
In this example, we will create an empty string stored in a variable “val”:

Then, we will use the length property in a conditional statement to check if the length of the variable is 0, representing that it is an empty string:

Execute the above code and see the output:

Let’s move to the next method!

Method 2: Check if a Variable is Null or Empty Using strict equality (===) and OR (||) Operator

Another method to verify the variable is null or empty is using the strict equality “===” operator with OR “||” operator. The strict equality operator checks the two operands of different types and returns a boolean value true if they are the same.

Syntax
You can use the following syntax for checking the variable is null or empty:

Example
Here, we will create a variable “val” and assigned a “null” value to it:

Then, we will use the OR operator with strict equality operator in the “if” conditional statement to verify whether the variable is null or empty:

The output indicates that the variable “val” is null:

We have presented all the methods to check if a variable is null or empty in JavaScript.

Conclusion

For verifying whether the variable is null or empty, you can use the length property of the JavaScript or the strict equality (===) operator with the OR (||) operator in JavaScript. The length property is mainly used for the empty variables because the empty variables contain 0 lengths while null shows the absence of object value. In this blog, we have discussed the methods for checking the variable, whether it is null or empty or not.

About the author

Farah Batool

I completed my master’s degree in computer science. I am an academic researcher and love to learn and write about new technologies. I am passionate about writing and sharing my experience with the world.

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Javascript Check 8 Ways To Verify If A Variable Is Empty Or Null

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JavaScript Check: How to Verify if a Variable is a Number?

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JavaScript Check: How to Verify if a String is Null or Empty

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Verify the length of a variable

div> Question: At the moment I have an if the condition that checks, lengths is greater than 2 if true check for another condition, else console.log the output., 34′; var current_data_change= «»; var current_data_end = «»; var current_data_profile = «normal»; // check, string_to_check = previous_data_change + current_data_start + current_data_end + current_data_profile; // check, I have seen such solutions, but they are extremely slow for longer length variables.

How to verify a check is good

Client checks Verify that the client was installed correctly , Verify the client service There are three checks for the SMS, Verify that client check has recently run Verify that the client, Verify WMI There are several checks specific to WMI., Verify Windows Update service This check verifies that the Windows

‘to check’ versus ‘to verify’

Check would simply sound more casual., that is not verifiable!, the adequacy of. ‘, better the agent should seek to verify. or check the adequacy., Another preferred technique is to assign the function’s return value to a temporary variable, and then test the variable in an ASSERT statement.

Python Check: How to Verify if a Variable is an Integer or Decimal?

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Javascript verify if variable is a string typescript

blockquote> When performing specific operations, you may face a situation that demands you to verify, First, we’ll take a look at how to check if a particular variable is a string in JavaScript and then, , the typeof operator is the most used method to check the type of any variable, if a variable is a string in JavaScript., This article will discuss checking if a variable is a string in TypeScript.

5 Methods to Verify if a Variable is an Array in JavaScript

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JavaScript jQuery Check: How to Verify If Input Value is Not Empty

JavaScript and jQuery., Using the .files property The .files property is a JavaScript, using-the-isnullorempty-method»>Using the IsNullOrEmpty() method The IsNullOrEmpty() method is a JavaScript, if input value is not empty with JavaScript and jQueryIn javascript,

Javascript verify if input is checked code example

What works now is checking the length of the element., the user input against the name of the image, first, make num a global variable, Here is the final code: var random_images_array,Visa Debit */ // Javascript, if input is checked javascript const cb

Javascript angular checkbox on checked verify

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JavaScript Check: 7 Methods to Verify if a Value is a String

if a variable is a string in JavaScript, each with its own advantages and disadvantages., To check if a value is a string, we can use typeof with the variable in question., We can use this method to check if a variable is a string., can be used to check if a variable is a number and a finite value., We can use this function to check if a variable is not a string.

Verify if variable is a number code example

The variable passed is for example var and %var% , strong> Solution: It’s generally not possible to directly compare variables, Since C++ is a typed language, the type you have used to declare a variable will always stay the same, You’ll need to check the state of your input stream, to test if the input was given in, This is only an example and you may have to check thoroughly and modify before

How to verify if a variable is empty in python

strong> Solution 1: Use .strip() to remove whitespace, and then check, With this script, it will only ever print the last line if both of my variables, if not all((name, loca)): Or, seeing as «all» it’s just 2 variables, What you want to do is check if the names have a non-empty value: if, Second, your if statement is checking

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