JavaScript String fromCodePoint() Method

What You’ll Learn

String.fromCodePoint() is a static helper (same API as MDN String.fromCodePoint()). It builds a string from full Unicode code points — including emoji — without manually writing surrogate pairs. Learn valid ranges, RangeError rules, how length can grow, and how it compares to fromCharCode() — with five examples and try-it labs.

Introduction

Unicode code points run from 0 to 0x10FFFF (over one million values). Everyday letters sit in the BMP (below 65536). Many emoji and rare characters sit higher and need two UTF-16 code units in memory.

fromCodePoint() lets you pass the real Unicode value — for example 0x1f303 for 🌃 — and JavaScript builds the correct UTF-16 storage for you. That is easier than looking up a surrogate pair for fromCharCode().

This page is part of JavaScript String Methods under Static Methods. Related topics include fromCharCode() and codePointAt().

Understanding the fromCodePoint() Method

Each argument is one Unicode code point. The method returns a string made of those characters in order. Unlike fromCharCode, invalid numbers throw instead of silently truncating.

• Valid integers: 0 … 0x10FFFF (inclusive).
• Non-integers, negatives, NaN, Infinity, or values above the max → RangeError.
• Supplementary characters may make result.length larger than the argument count.
• Pair with codePointAt() to round-trip full Unicode values.

📝 Syntax

General form of the static String.fromCodePoint method:

String.fromCodePoint()
String.fromCodePoint(num1)
String.fromCodePoint(num1, num2)
String.fromCodePoint(num1, num2, /* …, */ numN)

Parameters

• num1, …, numN — integers between 0 and 0x10FFFF (inclusive) representing Unicode code points.

Return value

A string created from the given code points. No arguments → "".

Exceptions

RangeError if any value is not a valid integer code point after conversion.

Common patterns

String.fromCodePoint(65, 90);       // "AZ"
String.fromCodePoint(0x1f303);      // "🌃"
String.fromCodePoint(0x2f804);      // "你"

// Round-trip with codePointAt:
String.fromCodePoint("🌃".codePointAt(0)); // "🌃"

// fromCharCode needs a surrogate pair for the same emoji:
String.fromCharCode(0xd83c, 0xdf03); // "🌃"

Examples Gallery

Examples follow MDN String.fromCodePoint() patterns. Use View Output or Try It Yourself for each case.

String.fromCodePoint(9731, 9733, 9842, 0x2f804);
// "☃★♲你"

☃★♲你

String.fromCodePoint(42);        // "*"
String.fromCodePoint(65, 90);    // "AZ"
String.fromCodePoint(0x404);     // "Є"

*
AZ
Є

String.fromCodePoint(0x1f303);           // "🌃"
String.fromCodePoint(127747);            // "🌃"  (decimal)

// Same character via fromCharCode (surrogate pair):
String.fromCharCode(0xd83c, 0xdf03);     // "🌃"

🌃
🌃
🌃

const s = String.fromCodePoint(0x1d306, 0x61, 0x1d307);
// "𝌆a𝌇"

s.length;                 // 5  (two pairs + "a")
[...s].length;            // 3  (three code points)
"🌃".length;               // 2
String.fromCodePoint(0x1f303).length; // 2

𝌆a𝌇
5
3
2
2

// String.fromCodePoint("_");      // RangeError
// String.fromCodePoint(Infinity); // RangeError
// String.fromCodePoint(-1);       // RangeError
// String.fromCodePoint(3.14);     // RangeError

String.fromCodePoint();            // ""

RangeError
RangeError
RangeError
RangeError
""

🚀 Common Use Cases

• Emoji / rare characters — pass the Unicode value directly (no surrogate math).
• Round-trip with codePointAt — store and rebuild full characters safely.
• Unicode tables / generators — loop code points in a known range.
• Safer than fromCharCode for U+10000+ — throws on invalid values instead of truncating.
• Teaching UTF-16 — show why length can be 2 for one visible character.
• Not for grapheme clusters — skin tones / ZWJ sequences are multiple code points.

📝 Notes

• Always call String.fromCodePoint(...) — it is static.
• Prefer it over fromCharCode() for values above 0xFFFF.
• Pair with codePointAt() for round-trips.
• Invalid numbers throw RangeError — they do not truncate.
• length counts UTF-16 units, not necessarily “visible characters.”
• Related: charCodeAt(), [Symbol.iterator]().

💡 Best Practices