For AI agents: the complete documentation index is available at /llms.txt, the full documentation bundle is available at /llms-full.txt, and this page is available as Markdown at /reference/string/upperFirst.md.
Install massaman

    upperFirst es-toolkit

    Converts the first character of a string to uppercase.

    const result = upperFirst(str);

    Usage

    upperFirst(str)

    Use upperFirst when you want to capitalize only the first letter of a string while keeping the rest of the letters unchanged. It's useful for capitalizing the beginning of sentences or formatting names.

    import { upperFirst } from 'es-toolkit/string';

// Capitalize the first letter of a lowercase string
upperFirst('fred');
// Returns: 'Fred'

// Keep the string as is if first letter is already uppercase
upperFirst('Fred');
// Returns: 'Fred'

// Keep the string as is even if all letters are uppercase
upperFirst('FRED');
// Returns: 'FRED'

    Useful in various situations:

    // Format user names
const userName = 'john';
const displayName = upperFirst(userName);
console.log(displayName); // 'John'

// Capitalize the first letter of a sentence
const sentence = 'hello world';
const capitalizedSentence = upperFirst(sentence);
console.log(capitalizedSentence); // 'Hello world'

// Process multiple names
const names = ['alice', 'bob', 'charlie'];
const capitalizedNames = names.map(name => upperFirst(name));
console.log(capitalizedNames); // ['Alice', 'Bob', 'Charlie']

// Convert camelCase to PascalCase
const camelCase = 'firstName';
const pascalCase = upperFirst(camelCase);
console.log(pascalCase); // 'FirstName'

    Parameters

    strstringrequired

    The string to capitalize the first letter of.

    Returns

    Returns a string with the first letter converted to uppercase.

    string
    Source: es-toolkit

    Re-exported verbatim from es-toolkit. Implementation, edge cases, and performance behavior are owned upstream. This page mirrors the documentation at the pinned version; the linked source is authoritative.