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Convert between binary and decimal numbers in JavaScript

Submitted by: @import:30-seconds-of-code·Mar 2, 2026·

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Problem

I don't often work with binary numbers, but whenever I do, I find myself looking up certain pieces of information over and over again. This is especially true when I need to convert a binary string to a decimal number or vice versa. Let's take a look at how to do this in JavaScript.
Given a binary string, you can use Number.parseInt() with a base of 2 to indicate the string is in binary format and convert it to its decimal equivalent.
You may also use the BigInt constructor to convert a binary string to a BigInt. This is useful when dealing with very large numbers that exceed the range of regular integers.
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Solution

const binaryToDecimal = binary => Number.parseInt(binary, 2);

binaryToDecimal('10');  // 2
binaryToDecimal('110'); // 6

You may also use the BigInt constructor to convert a binary string to a BigInt. This is useful when dealing with very large numbers that exceed the range of regular integers.
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> Notice the 0b prefix in the string passed to BigInt? This prefix indicates that the string is a binary number. In fact, you can use this in your code when writing out a numeric value in binary, like this:
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Code Snippets

const binaryToDecimal = binary => Number.parseInt(binary, 2);

binaryToDecimal('10');  // 2
binaryToDecimal('110'); // 6

const binaryToBigInt = binary => BigInt(`0b${binary}`);

binaryToBigInt('10');   // 2n
binaryToBigInt('110');  // 6n

> const binaryNumber = 0b10;        // 2 (Number)
> const bigIntBinaryNumber = 0b10n; // 2n (BigInt)
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Context

From 30-seconds-of-code: binary-number-conversion

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