JavaScript toLowerCase(): Convert Text to Lowercase

The toLowerCase() method returns a new string with letters converted to lowercase. It does not change the original string.

const text = "Welcome To Plus2net";
const lower = text.toLowerCase();
console.log(lower); // welcome to plus2net

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toLowerCase() syntax Top ↑

string.toLowerCase()

The method takes no arguments and returns a new string.

Original string is unchanged Top ↑

const original = "JavaScript";
const changed = original.toLowerCase();
console.log(original); // JavaScript
console.log(changed);  // javascript

Strings are immutable, so store the returned value when you need the converted text.

Convert user input as it is typed Top ↑

Result:

const input = document.getElementById('lowerDemo');
input.addEventListener('input', () => {
  result.textContent = input.value.toLowerCase();
});

This modernizes the original onKeyUp demo while keeping the same teaching goal. See keyboard event handling.

Case-insensitive comparisons Top ↑

const a = "JavaScript";
const b = "javascript";
console.log(a.toLowerCase() === b.toLowerCase()); // true

Normalizing both values is useful for simple case-insensitive comparisons.

Locale-sensitive case conversion Top ↑

const city = "İSTANBUL";
console.log(city.toLocaleLowerCase("tr"));

For language-sensitive casing, consider toLocaleLowerCase().

Common mistakes Top ↑

Do not expect the original variable to change automatically, and do not use lowercase conversion as a substitute for full locale-aware collation or security normalization.

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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.

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