JavaScript String length

Posted in JavaScript Tutorial

Updated on Oct 04, 2024

By Mari Selvan

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⏳ 4 mins

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Photo Credit to CodeToFun

Introduction

The length property in JavaScript is a built-in property that returns the number of characters in a string.

It's a simple and effective way to determine the size of a string, making it useful for tasks like input validation, string manipulation, and more.

Understanding the length Property

The length property is an integer that reflects the number of 16-bit units (or characters) present in a string. This includes letters, digits, symbols, whitespace, and any special characters, with each counting as a single unit.

JavaScript

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const str = "Hello, World!";
console.log(str.length); // Output: 13

How to Use the length Property

Using the length property is straightforward. It can be accessed directly on any string and is often used to determine if a string meets a specific length requirement.

JavaScript

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const password = "mypassword";
if (password.length >= 8) {
  console.log("Password length is sufficient.");
} else {
  console.log("Password is too short.");
}

Common Use Cases

Input Validation: Check if user input meets required length criteria.
Substring Extraction: Determine how much of a string to extract or manipulate.
Looping Over Characters: Use length in a loop to iterate over each character in a string.
Truncating Strings: Shorten strings that exceed a specific length.

Important Considerations

Multibyte Characters:

length counts UTF-16 code units, so characters like emojis or special symbols that use surrogate pairs may not be counted accurately. For instance:
JavaScript
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```
const emoji = "💖";
console.log(emoji.length); // Output: 2
```
Whitespace:

Spaces, tabs, and newline characters all contribute to a string's length.
Immutable Property:

The length property is read-only. You cannot directly change the length of a string as strings in JavaScript are immutable.

Example

Here’s a basic example that demonstrates how to use length to create a character counter for a text input:

HTML

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<!DOCTYPE html>
<html>
<head>
  <title>String Length Example</title>
</head>
<body>
  <h1>Character Counter</h1>
  <textarea id="textInput" rows="4" cols="50"></textarea>
  <p id="charCount">Characters: 0</p>

  <script>
    const textarea = document.getElementById('textInput');
    const charCount = document.getElementById('charCount');

    textarea.addEventListener('input', () => {
      const length = textarea.value.length;
      charCount.textContent = 'Characters: ' + length;
    });
  </script>
</body>
</html>

Conclusion

The length property is an essential tool for handling and manipulating strings in JavaScript. With its simple syntax and versatility, it's a go-to for many string-related tasks. Understanding its behavior, especially with multibyte characters and whitespace, will help you use it effectively in your projects.