How to check for null values in JavaScript ?

The null values show the non-appearance of any object value. It is usually set on purpose to indicate that a variable has been declared but not yet assigned any value. This contrasts null from the similar primitive value undefined, which is an unintentional absence of any object value. That is because a variable that has been declared but not assigned any value is undefined, not null.

Below are the approaches:

Approach 1: By equality Operator (===)

By this operator, we will learn how to check for null values in JavaScript by the (===) operator. This operator only passes for null values, not for undefined, false, 0, NaN.

Syntax:

x === y;

Example: The following code snippets show some comparison of objects.

Javascript

const object1 = {
        key: "value",
    };

    const object2 = {
        key: "value",
    };

    console.log(object1 === object2);
    console.log(object1 === object1);

Output

false
true

Approach 2: By Object.is() function

This function checks whether two objects’ values are equal or not. If they are the same the two object’s values are the same if both values are null.

Syntax:

Object.is( a, null )'

Example: In this example, we are using Object.is() function.

Javascript

let maybeNull = null

    // The following is equivalent to
    // maybeNull == null
    // or maybeNull == undefined:
    console.log(Object.is(maybeNull, undefined)
        || Object.is(maybeNull, null))

    // Compare to the following:
    console.log(maybeNull == null)
    console.log(maybeNull == undefined)
    console.log(maybeNull === null)
    console.log(Object.is(maybeNull, null))
    console.log(maybeNull === undefined)
    console.log(Object.is(maybeNull, undefined))

    maybeNull = undefined
    console.log(maybeNull === undefined || maybeNull === null)
    console.log(maybeNull == null)
    console.log(maybeNull == undefined)
    console.log(maybeNull === null)
    console.log(Object.is(maybeNull, null))
    console.log(maybeNull === undefined)
    console.log(Object.is(maybeNull, undefined))

Output

true
true
true
true
true
false
false
true
true
true
false
false
true
true

Approach 3: By the typeof Operator

Using typeof operator is very useful because if a variable is not declared, it will show ReferenceError. But, the typeof a non-declared value is undefined, so using the typeof is a better way to check for null and undefined variables.

Syntax:

typeof var;

Example: In this example, we are using typeof Operator.

Javascript

// This will safely check a value to make sure it
// has been declared and assigned a value other
// than null or undefined:
console.log(typeof undeclaredVariable !== "undefined"
    && (typeof undeclaredVariable !== "object"
        || !undeclaredVariable))

// Compare to checking for null using ==,
// which will only work for declared variables:
try { undeclaredVariable == null }
catch (e) { console.log(e) }
try { undeclaredVariable === null }
catch (e) { console.log(e) }
try { undeclaredVariable === undefined }
catch (e) { console.log(e) }

let declaredButUndefinedVariable
// Values that have been declared but not
// assigned a value will have the value
// undefined, which has a typeof undefined
console.log(typeof declaredButUndefinedVariable
    !== "undefined" &&
    (typeof declaredButUndefinedVariable !== "object"
        || !declaredButUndefinedVariable))

let stringVariable = "Here's Johnny!"

// If the variable has been both declared and
// assigned a value that is neither null or undefined,
// we will get true.
console.log(typeof stringVariable !== "undefined" &&
    (typeof stringVariable !== "object" || !stringVariable))

// This can be used to create a function that will return
// false for undefined, undeclared, and null values.
const isNotNullNorUndefined =
    (value) => typeof value !== "undefined"
    && (typeof value !== "object" || !value)
console.log(isNotNullNorUndefined(stringVariable))

Output

...js:7:7)
    at Module._compile (node:internal/modules/cjs/loader:1155:14)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1209:10)
    at Module.load (node:internal/modules/cjs/loader:1033:32)
    at Function.Module._load (node:internal/modules/cjs/loader:868:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)
    at node:internal/main/run_main_module:22:47
ReferenceError: undeclaredVariable is not defined
    at Object.<anonymous> (/home/guest/sandbox/55da4d93-5c09-4cd3-8be9-a1459e8ed1b0.js:8:7)
    at Module._compile (node:internal/modules/cjs/loader:1155:14)
    at Object.Module._extensions..js (node:internal/modules/cjs/loader:1209:10)
    at Module.load (node:internal/modules/cjs/loader:1033:32)
    at Function.Module._load (node:internal/modules/cjs/loader:868:12)
    at Function.executeUserEntryPoint [as runMain] (node:internal/modules/run_main:81:12)
    at node:internal/main/run_main_module:22:47
false
true
true

Approach 4: Using Lodash _.isNull() Method

Lodash _.isNull() method is used to find whether the value of the object is null. If the value is null then returns true otherwise it returns false.

Syntax:

_.isNull(value);

Example: In this example, we are checking whether the given value is null or not by the use of the _isNull() method.

Javascript

// Requiring the lodash library
const _ = require("lodash");

// Use of _.isNull()
// method
let gfg = _.isNull(null);
let gfg1 = _.isNull(void 0);

// Printing the output
console.log(gfg);
console.log(gfg1);

Output:

true
false