Not null string javascript

How do I Check for an Empty/Undefined/Null String in JavaScript?

You want to check that a value is not an empty string, null, or undefined. How do you do this?

To check that a value is not an empty string, null, or undefined, you can create a custom function that returns true if a value is null , undefined , or an empty string and false for all other falsy values and truthy values:

function isEmpty(value) < return (value == null || (typeof value === "string" && value.trim().length === 0)); >console.log(isEmpty("cat")); // false console.log(isEmpty(1)); // false console.log(isEmpty([])); // false console.log(isEmpty(<>)); // false console.log(isEmpty(false)); // false console.log(isEmpty(0)); // false console.log(isEmpty(-0)); // false console.log(isEmpty(NaN)); // false console.log(isEmpty("")); // true console.log(isEmpty(" ")); // true console.log(isEmpty(null)); // true console.log(isEmpty(undefined)); // true Click to Copy 

The isEmpty function uses the equality operator ( == ) to check if the argument value is null or undefined . This works because if one of the operands is null or undefined , the other operand must be null or undefined for the equality comparison to return true . If the argument value is not null or undefined , the right side of the logical OR (||) operator is evaluated.

To check for an empty string, the logical && operator is used. The first operand uses the typeof operator to check if the argument value is a string. If the value is a string, leading and trailing white space and line terminator strings are removed using the trim() method. This logical && operator expression returns true if a string is empty or consists of white space and line terminator strings only.

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How to Check for Empty/Undefined/Null String in JavaScript

In JavaScript, one of the everyday tasks while validating data is to ensure that a variable, meant to be string, obtains a valid value.

This snippet will guide you in finding the ways of checking whether the string is empty , undefined , or null .

If you want to check whether the string is empty/null/undefined, use the following code:

let emptyStr; if (!emptyStr) < // String is empty >

Javascript empty string

When the string is not null or undefined, and you intend to check for an empty one, you can use the length property of the string prototype, as follows:

Javascript empty string

Another option is checking the empty string with the comparison operator “===” .

It’s visualized in the following example:

Javascript empty string

Description of Strings in JavaScript

The JavaScript strings are generally applied for either storing or manipulating text. There is no separate for a single character. The internal format of the strings is considered UTF-16.

Another vital thing to know is that string presents zero or more characters written in quotes.

Usage of the Length Property in JavaScript

The “length” property is an essential JavaScript property, used for returning the number of function parameters. Also, the “length” property can be used for introspecting in the functions that operate on other functions.

Comparison Operators in JavaScript

Comparison operators are probably familiar to you from math.

So, they are the following:

• Less than ( ) : returns true when the value on the left is greater than the one on the right. Otherwise, it will return false.
• Less than or equal to ( =) : returns true when the value on the left is greater or equal to the one on the right. In another way, it will return false.
• Equal to (===) : returns true when the value on the left is equal to the one on the right. Otherwise, it will return false.
• Not equal to (!==) : returns true when the value on the left is not equal to the one on the right. In another way, it will return false.

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JavaScript Check Empty String – Checking Null or Empty in JS

Joel Olawanle

There are a number of reasons why you might need to check if a string is empty or not. One of the most important reasons is when you’re retrieving data from a database, API, or input field.

In this article, you will learn how to check if a sting is empty or null in JavaScript. We will see many examples and methods you can use so that you can understand them and decide which one to use and when.

What’s the Difference Between Null and Empty?

Before we begin, you need to understand what the terms Null and Empty mean, and understand that they are not synonymous.

For example, if we declare a variable and assign it an empty string, and then declare another variable and assign it the Null value, we can tell them apart by looking at their datatype:

let myStr1 = ""; let myStr2 = null; console.log(typeof myStr1); // "string" console.log(typeof myStr2); // "object" 

Looking at the code above, we can see that the compiler/computer interprets each value differently. So when it comes time to check, we must pass conditions for both types of values because we as humans frequently refer to null as empty.

How to Check for Empty or Null in JavaScript

We now know that an empty string is one that contains no characters. It is very simple to check if a string is empty. We can use two major methods that are somewhat similar because we will use the strict equality operator ( == ).

How to Check for an Empty String in JavaScript with the length Property

In this first method, we will check for the length of the string by adding the length property. We’ll check if the length is equal to 0 . If it’s equal to zero, it means that the string is empty, as we can see below:

let myStr = ""; if (myStr.length === 0)

The above will return this:

But this approach unfortunately might not work in all situations. For example, if we have a string that has white spaces as seen below:

let myStr = " "; if (myStr.length === 0) < console.log("This is an empty string!"); >else

"This is NOT an empty string!" 

We can easily fix this error by first removing the white spaces using the trim() method before checking for the length of such string to see if it’s empty as seen below:

let myStr = " "; if (myStr.trim().length === 0) < console.log("This is an empty string!"); >else

This will now return the following:

Note: If the value is null, this will throw an error because the length property does not work for null.

To fix this, we can add an argument that checks if the value’s type is a string and skips this check if it is not:

let myStr = null; if (typeof myStr === "string" && myStr.trim().length === 0)

How to Check for an Empty String in JavaScript by String Comparison

Another way to check if a string is empty is by comparing the string to an empty string.

As with the previous method, if we have white spaces, this will not read the string as empty. So we must first use the trim() method to remove all forms of whitespace:

let myStr = " "; if (myStr.trim() === "") < console.log("This is an empty string!"); >else

Just as we did for the length method, we can also check for the type of the value so that this will only run when the value is a string:

let myStr = null; if (typeof myStr === "string" && myStr.trim() === "")

How to Check for Null in JavaScript

So far, we’ve seen how to check if a string is empty using the length and comparison methods.

Now, let’s see how to check if it’s null , and then check for both. To check for null , we simply compare that variable to null itself as follows:

let myStr = null; if (myStr === null)

How to Check for a Null or Empty String in JavaScript

At this point we have learned how to check for an empty string and also if a variable is set is null. Let’s now check to for both this way:

let myStr = null; if (myStr === null || myStr.trim() === "") < console.log("This is an empty string!"); >else

Conclusion

In this article, we learned how to check for an empty string or null and why they are not the same thing.

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How to Check if a String is Empty or Null in JavaScript – JS Tutorial

Joel Olawanle

In JavaScript, it’s important to check whether a string is empty or null before performing any operation. Trying to operate on an empty or null string can lead to errors, bugs, and unexpected results.

In this tutorial, we’ll explore the different ways of checking whether a string is empty or null in JavaScript and some best practices to follow when doing so.

What are Empty and Null Strings?

An empty string is a string that has no characters, while a null string is a string that has no value assigned to it. It’s important to differentiate between the two, as they are not the same.

For example, you have a form where a user can input their name. If the user doesn’t input anything, the input field’s value will be an empty string. However, the value will be null if the input field is not even created.

How to Check for Empty or Null Strings

JavaScript has several ways to check whether a string is empty or null. Let’s explore some of them.

Using the if Statement and typeof Operator

One way to check for an empty or null string is to use the if statement and the typeof operator. Here’s an example:

let str = ""; if (typeof str === "string" && str.length === 0) < console.log("The string is empty"); >else if (str === null) < console.log("The string is null"); >else

In this example, we’re checking whether the str variable is a string and whether its length is zero. If it is, then we know that it’s an empty string. If the str variable is null , then we know that it’s a null string. Otherwise, we know that the string is not empty or null.

Using the length Property

Another way to check for an empty string is to use the length property. Here’s an example:

let str = ""; if (str.length === 0) < console.log("The string is empty"); >else

In this example, we’re checking whether the str variable’s length is zero. If it is, then we know that it’s an empty string. Otherwise, we know that the string is not empty.

Using the trim Method

Sometimes, a string might contain whitespace characters that make it appear non-empty even when it is. In such cases, we can use the trim method to remove any leading or trailing whitespace characters before checking for emptiness. Here’s an example:

let str = " "; if (str.trim().length === 0) < console.log("The string is empty"); >else

In this example, we’re first using the trim method to remove any leading or trailing whitespace characters from the str variable, then checking whether the resulting string has zero length. If it does, then we know that the string is empty. Otherwise, we know that the string is not empty.

Best Practices for Checking Empty or Null Strings

Here are some best practices to follow when checking for empty or null strings in JavaScript:

• Always use triple equals ( === ) when comparing a string to null . This ensures that the types are checked, and you don’t accidentally compare a string to the number 0 or false .
• Use strict equality ( === ) when checking for an empty string. This ensures you don’t compare an empty string to a string containing only whitespace characters.
• Use the trim method to remove leading and trailing whitespace characters before checking for an empty string. This ensures that strings with only whitespace characters are also considered empty.
• Use regular expressions for more complex checks, such as checking for a string that only contains digits or checking for a string that matches a certain pattern.

let str = "12345"; let digitRegExp = /^\d+$/; if (digitRegExp.test(str)) < console.log("The string contains only digits"); >else

Conclusion

In this article, we’ve learned how to check whether a string is empty or null in JavaScript. We’ve explored different methods for doing so, such as using the if statement and typeof operator, the length property, and the trim method.

If you would like to learn more about JavaScript and web development, browse 200+ expert articles on web development written by me, and also check out my blog for more captivating content.

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