How to Check If String is empty/undefined/null in JavaScript

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To check if a string is empty/undefined/null in JavaScript, you can use the “! operator” that returns true for empty strings, undefined values, null values, and other false values.

Example 1

function isEmpty(str) {
  return !str;
}

const emptyString = '';
const nullValue = null;
const undefinedValue = undefined;
const nonEmptyString = 'Hello, world!';

console.log(isEmpty(emptyString));
console.log(isEmpty(nullValue));
console.log(isEmpty(undefinedValue));
console.log(isEmpty(nonEmptyString));

Output

true
true
true
false

This approach also considers other falsy values (e.g., 0, false, and NaN) to be “empty”, which may not be suitable for all use cases.

Example 2

You can use a more explicit conditional check to check specifically for empty strings, undefined values, or null values.

function isEmpty(str) {
  return str === '' || str === null || str === undefined;
}

const emptyString = '';
const nullValue = null;
const undefinedValue = undefined;
const nonEmptyString = 'Hello, world!';

console.log(isEmpty(emptyString));
console.log(isEmpty(nullValue));
console.log(isEmpty(undefinedValue));
console.log(isEmpty(nonEmptyString));

Output

true
true
true
false

This function checks if the given value is an empty string, null, or undefined and returns true if any conditions are met.

How to check if a string is empty

To check if a string is empty(only empty), compare its “length property to 0” or directly compare it to an “empty string (‘ ‘)”.

Method 1: Comparing its length to 0

You can compare the string’s length to 0. If it is, it returns true otherwise, it is false.

const emptyString = "";
const nonEmptyString = "Harry, Potter!";

if (emptyString.length === 0) {
  console.log("emptyString is empty");
} else {
  console.log("emptyString is not empty");
}

if (nonEmptyString.length === 0) {
  console.log("nonEmptyString is empty");
} else {
  console.log("nonEmptyString is not empty");
}

Output

emptyString is empty

nonEmptyString is not empty

Method 2: Comparing a string to an empty string

You can compare an input string directly to an empty string.

const emptyString = "";
const nonEmptyString = "Harry, Potter!";

if (emptyString === "") {
  console.log("emptyString is empty");
} else {
  console.log("emptyString is not empty");
}

if (nonEmptyString === "") {
  console.log("nonEmptyString is empty");
} else {
  console.log("nonEmptyString is not empty");
}

Output

emptyString is empty

nonEmptyString is not empty

Both of these methods work great for checking if a string is empty.

Using the length property is often preferred since it’s more explicit, and it can also be used to check for strings containing only whitespace characters using the trim() method.

const stringWithSpaces = " ";

if (stringWithSpaces.trim().length === 0) {
  console.log("stringWithSpaces is empty or contains only whitespace");
} else {
  console.log("stringWithSpaces is not empty");
}

Output

stringWithSpaces is empty or contains only whitespace

In this code, the trim() method removes whitespace characters from the beginning and end of the string, and the length property is used to check if the resulting string is empty.