JavaScript Number Base Conversion

JavaScript can convert Number values to bases from 2 through 36 with toString(radix), and parse text written in another base with parseInt(text, radix).

const decimal = 255;
console.log(decimal.toString(16)); // "ff"
console.log(parseInt("ff", 16)); // 255

Show Table of Contents ↓

Common number bases Top ↑

Decimal uses base 10, binary uses base 2, octal uses base 8, and hexadecimal uses base 16. Hexadecimal digits after 9 are represented by a through f. Web colors often use hexadecimal notation such as #0000ff.

Decimal, hexadecimal, octal and binary examples Top ↑

Convert decimal to binary, octal or hexadecimal Top ↑

const n = 255;
console.log(n.toString(2));  // "11111111"
console.log(n.toString(8));  // "377"
console.log(n.toString(16)); // "ff"

Convert binary, octal or hexadecimal text to decimal Top ↑

console.log(parseInt("11111111", 2)); // 255
console.log(parseInt("377", 8));      // 255
console.log(parseInt("ff", 16));      // 255

See parseInt() for detailed radix rules.

JavaScript supports radixes from 2 through 36 Top ↑

console.log((35).toString(36)); // "z"

A radix outside 2–36 causes Number.prototype.toString() to throw a RangeError.

Negative values keep their sign Top ↑

console.log((-15).toString(2)); // "-1111"

This is a signed textual representation, not a two's-complement bit pattern.

Invalid digits and NaN Top ↑

const value = parseInt("102", 2);
console.log(value); // 2 because parsing stops before the invalid digit 2

If you require the entire input to be valid for a base, validate the string before parsing instead of relying only on parseInt().

Large integer precision Top ↑

These conversions return ordinary JavaScript Numbers, so values beyond the safe-integer range can lose integer precision. Use BigInt when an exact very large integer is required and the surrounding application supports it.

Decimal and hexadecimal conversion Top ↑

Continue with the dedicated decimal to hexadecimal and hexadecimal to decimal tutorial.

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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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