Not null object javascript

Javascript Check If an Object Is Null or Undefined

While working in javascript, often we encounter a requirement that is to determine if the object is null or not. We might require this check to verify that the object is not null when the objects are loaded dynamically. If the value of the object is not null or not undefined, only then perform operations on it. This article discusses various ways to check if an object is null or undefined using example illustrations.

Javascript objects are something that describes anything with properties and methods.

The null keyword in javascript primitive data means that there is no value. If an object is null, it will not have any value.

The undefined keyword in javascript means not defined. If an object is undefined, it means that it has not been assigned any value.

Frequently Asked:

Check if the below objects are null or undefined

// function to check if the object is undefined or null function checkIfObjectIsNull(_object) < if (_object === undefined || _object === null) < console.log("Object Is Null Or Undefined"); >else < console.log("Object Is Ok"); >> let personObject1 = < personFirstName : 'George', personLastName : 'Smith', dateOfBirth : 'Nov 14 1984' , city : 'Santiago' >; let personObject2 ; let personObject3 = null ; let personObject4 = <>; // usage of the function to check for the objects checkIfObjectIsNull(personObject1); checkIfObjectIsNull(personObject2); checkIfObjectIsNull(personObject3); checkIfObjectIsNull(personObject4);

Object Is Ok Object Is Null Or Undefined Object Is Null Or Undefined Object Is Ok

Explanation:-

• Here, we are checking 4 different objects. Let’s see how the results differ.
• personObject1is not null nor unde fined hence n one of the checks are passed in the if statement (_object === undefined || _object === null).
• personObject2 is not null but undefined as the object is declared, but no value is assigned to it. Doing any operation on it will give an error that the object is undefined. Hence, it passes the check (_object === undefined)
• personObject3 is null. We are explicitly assigning the value null to the object. Hence, it passes the check (_object === null)
• personObject4, for this object, we get the output ‘Object Is Ok ‘ as the object is defined and is not null. Here the object is empty. That is there are no properties and methods defined in this object. Hence, none of the checks are passed in the if statement.

Using typeOf to check if the object is null or undefined

Javascript’s typeOf operator will return a string representing the type of the operand.

Here op is the operand whose type is determined.

Check if the below objects are null or undefined

// function to check if the object is undefined or null function checkIfObjectIsNull(_object) < if (typeof _object === "object" && _object !== null) < console.log("Object Is Ok"); >else < console.log("Object Is Null or Undefined"); >> let personObject1 = < personFirstName : 'George', personLastName : 'Smith', dateOfBirth : 'Nov 14 1984' , city : 'Santiago' >; let personObject2 ; let personObject3 = null ; let personObject4 = <>; // usage of the function to check for the objects checkIfObjectIsNull(personObject1); checkIfObjectIsNull(personObject2); checkIfObjectIsNull(personObject3); checkIfObjectIsNull(personObject4);

Object Is Ok Object Is Null or Undefined Object Is Null or Undefined Object Is Ok

Explanation:-

• Here, the output for personObject1 and personObject4 is “Object Is Ok” because:
• personObject1 gets passed for both the checks (typeof _object === “object” && _object !== null) as it has the object declared and defined.
• personObject2 is not null but undefined, hence is not able to pass (typeof _object === “object” ) .
• personObject3 is null and hence fails the check (_object !== null) . Here we are using ‘!==’ operator which is a strict equalityoperator to confirm that the variable is not null.
• personObject4, since this object is only empty it is able to pass both the checks of the if statement.

I hope this article helped you check if the object is null or undefined. Good Luck .

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Not null object javascript

Last updated: Dec 27, 2022
Reading time · 4 min

# Check if a Variable is Not NULL in JavaScript

Use the strict inequality (!==) operator to check if a variable is not null, e.g. myVar !== null .

The strict inequality operator will return true if the variable is not equal to null and false otherwise.

Copied! 
const a = 'hello'; // ✅ check if a variable is NOT null if (a !== null)  // 👇️ this runs console.log('the variable is NOT null'); > else  console.log('the variable is null'); > // ------------------------------------- // ✅ check if a variable is NOT null and undefined if (a != null)  // 👇️ this runs console.log('the variable is NOT null and undefined'); > else  console.log('The variable is null or undefined'); > // ------------------------------------- // ✅ check if a variable has been declared (without errors) if (typeof abcd !== 'undefined')  console.log('The variable has been declared'); > else  // 👇️ this runs console.log('The variable is undeclared or set to undefined'); > 

We used the strict inequality (!==) operator to check if the value stored in a variable is not equal to null .

The operator returns a boolean result:

Copied! 
console.log(null !== null); // 👉️ false console.log('hello' !== null); // 👉️ true 

The strict inequality (!==) operator considers two values of different types to be different, as opposed to the loose inequality (!=) operator.

This means that if you compare null with any other type, the strict inequality (!==) operator will always return false .

A very common mistake is to check if a value is truthy , instead of checking if it’s not null. Here’s an example.

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const a = 'hello'; if (a)  console.log(`🚨 a is NOT false, 0, empty string, null, undefined, NaN`); > else  console.log(`⛔️️ a is ONE OF false, 0, empty string, null, undefined, NaN`); > 

In this example, we check if the value stored in the variable a is truthy. Truthy are all values that are not falsy.

The falsy values in JavaScript are: false , 0 , «» , null , undefined , NaN .

If the else block runs, the value of the variable is falsy and could be either of the 6 falsy values and not necessarily null .

Things could go wrong in many different ways when doing this. For example, if the value of a is equal to 0 , the else block would run.

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const a = 0; if (a)  console.log("⛔️ This doesn't run"); > else  console.log('✅ This runs'); > 

Even if this is what you want, it is better to be explicit.

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const a = 0; if (a === 0)  console.log('✅ This runs'); > else  console.log("⛔️ This doesn't run"); > 

It’s always recommended to explicitly use the strict operators (!==, ===) when making equality comparisons. They make your code more readable, explicit and less prone to errors.

One exception is when you need to check if a variable is not nullish.

# Check if a variable is NOT nullish in JavaScript

Here are 2 examples of checking if a variable is not nullish ( null and undefined ).

Copied! 
const a = 'hello'; // ✅ check if a variable is NOT null and undefined if (a != null)  // 👇️ this runs console.log('the variable is NOT null and undefined'); > else  console.log('The variable is null or undefined'); > // ------------------------------------- // ✅ check if a variable is NOT nullish (null and undefined) if (a !== null && a !== undefined)  // 👇️ this runs console.log('the variable is NOT null and undefined'); > else  console.log('The variable is null or undefined'); > 

The first example uses the loose inequality (!=) operator.

Copied! 
const a = 'hello'; if (a != null)  // 👇️ this runs console.log('the variable is NOT null and undefined'); > else  console.log('The variable is null or undefined'); > 

The expression a != null checks if the variable a is not equal to both null and undefined .

When using the loose equality (==) operator, null is equal to undefined .

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// 👇️ loose equality console.log(null == undefined); // 👉️ true // 👇️ strict equality console.log(null === undefined); // 👉️ false 

An alternative approach to check if a variable is not nullish ( null and undefined ) is to be explicit and use the logical AND (&&) operator.

Copied! 
const a = 'hello'; if (a !== null && a !== undefined)  // 👇️ this runs console.log('the variable is NOT null and undefined'); > else  console.log('The variable is null or undefined'); > 

We used the logical AND (&&) operator, so for the if block to run, both conditions have to be met.

The first condition checks if the variable is not equal to null and the second checks if the variable is not equal to undefined .

# Check if a variable has been declared in JavaScript

Use the typeof operator to check if a variable has been declared.

The typeof operator won’t throw an error even if the variable has not been declared.

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if (typeof abcd !== 'undefined')  console.log('The variable has been declared'); > else  // 👇️ this runs console.log('The variable is undeclared or set to undefined'); > 

Notice that the abcd variable has not been declared, but no error occurs when running the code sample.

The typeof operator returns a string that indicates the type of a value.

Once you find that the variable has been declared, you can check if the variable is not null .

Copied! 
if (typeof abcd !== 'undefined')  console.log('The variable has been declared'); if (abc !== null)  console.log('The variable is not null'); > else  console.log('The variable is null'); > > else  // 👇️ this runs console.log('The variable is undeclared or set to undefined'); > 

Once we enter the if block, we know that the variable has been declared and we can safely access it.

The inner if statement checks if the variable is not null .

Which approach you pick is a matter of personal preference. I always use the direct not null check — if (a !== null) <> .

In my experience, it’s better to be explicit even if it makes your code more verbose.

Getting an error is not necessarily a bad thing because most of the time, it surfaces a bug in your application.

I wrote a book in which I share everything I know about how to become a better, more efficient programmer.

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Функция для проверки на null, undefined или пустые переменные в JavaScript

В JavaScript, есть случаи, когда необходимо проверить, имеет ли переменная какое-либо значение или она является null , undefined или пустым значением. Особенно это актуально при обработке входных данных или при работе с внешними API.

Допустим, есть код, который обрабатывает данные, пришедшие из внешнего источника. Но эти данные могут быть непредсказуемыми, и иногда они могут быть null , undefined или просто пустыми. Это может привести к непредвиденным ошибкам в коде.

let data = getDataFromSource(); // может вернуть любое значение processData(data); // если data является null, undefined или пустым, здесь может произойти ошибка

В таких случаях, может быть полезно иметь универсальную функцию, которая проверяет, имеет ли переменная какое-либо значение или она является null , undefined или пустым значением.

Эта функция возвращает false , если значение val является undefined , null или пустой строкой, и true во всех остальных случаях.

Теперь, используя эту функцию, можно сделать код более безопасным:

let data = getDataFromSource(); // может вернуть любое значение if (isValue(data)) < processData(data); // будет вызвано только если data имеет значение >else < handleEmptyData(); // обрабатывает ситуацию, когда data не имеет значения >

Таким образом, функция проверки на null , undefined или пустые значения может быть полезной для обеспечения безопасности и надежности кода.

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