JavaScript String length Property

The JavaScript length property returns the number of UTF-16 code units in a string. It is available directly on every string value.

const text = "Hello world!";
console.log(text.length); // 12

Spaces and punctuation count because they are part of the string.

String length Syntax Top ↑

string.length

length is a property, not a function, so do not write length().

Length of an Empty String Top ↑

const empty = "";
console.log(empty.length); // 0

Last Character and Valid String Indexes Top ↑

Indexes start at 0, so the final valid index is length - 1.

const word = "JavaScript";
console.log(word[word.length - 1]); // t

Count Characters Entered by a User Top ↑

This modernizes the original page demo without inline JavaScript handlers.

const input = document.getElementById("text1");
const message = document.getElementById("msg");

document.getElementById("checkLength").addEventListener("click", () => {
  message.textContent = `The length of data = ${input.value.length}`;
});

String Length with Emoji and Unicode Top ↑

length counts UTF-16 code units, not always visible characters. Some emoji and other characters use two code units.

const symbol = "😀";
console.log(symbol.length);          // 2
console.log([...symbol].length);     // 1 code point

Even spread syntax counts Unicode code points rather than every possible user-perceived grapheme cluster, so complex emoji sequences can still require Intl.Segmenter when exact visual-character counting matters.

Length Before and After trim() Top ↑

const value = "  hello  ";
console.log(value.length);        // 9
console.log(value.trim().length); // 5

Common String length Mistakes Top ↑

• Calling length() as though it were a method.
• Forgetting that spaces and punctuation count.
• Using text[text.length] for the last character instead of text[text.length - 1].
• Assuming UTF-16 code-unit length always equals visible character count.

← String Reference Uppercase Strings →

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

About the author   Watch on YouTube

Connect: