Reverse Text in JavaScript

Reversing Strings in JavaScript

JavaScript offers several approaches to string reversal, each with different tradeoffs for readability, performance, and Unicode correctness.

Method 1: Split-Reverse-Join (Classic)

const reversed = str.split("").reverse().join("");

Warning: This breaks with emoji and surrogate pairs because split("") splits on UTF-16 code units, not Unicode code points.

"Hello 👋".split("").reverse().join("");
// "�👋 olleH" — broken!

Method 2: Spread Operator (Unicode-Safe)

const reversed = [...str].reverse().join("");

The spread operator iterates over Unicode code points, correctly handling emoji and multi-byte characters:

[..."Hello 👋"].reverse().join("");
// "👋 olleH" — correct!

Method 3: Array.from (Unicode-Safe)

const reversed = Array.from(str).reverse().join("");

Equivalent to the spread operator approach.

Method 4: For Loop

function reverse(str) {
  let result = "";
  for (let i = str.length - 1; i >= 0; i--) {
    result += str[i];
  }
  return result;
}

Note: This also has the UTF-16 surrogate pair issue. Use for...of for Unicode safety:

function reverse(str) {
  let result = "";
  for (const char of str) {
    result = char + result;
  }
  return result;
}

Method 5: Reduce

const reversed = [...str].reduce((acc, char) => char + acc, "");

Performance Comparison

For typical strings (< 10,000 characters), all methods perform similarly. For very large strings, the for-loop approach with pre-allocated array is fastest. The spread + reverse + join method offers the best balance of correctness and readability.