Convert Binary to Decimal – Mastering JS

Feb 11, 2022

A binary number is a number expressed in base-2, as opposed to conventional decimal numbers in base-10.

Below is a live calculator.

We also have a tool to convert decimal to binary.

How the Calculator Works

Converting binary numbers to decimal is easy.
For example, let x = '101010' creates a new variable x that contains the number as a string 101010.
JavaScript has a parseInt() method that takes a binary and radix parameter, and returns a number.
Calling parseInt(binary, radix) tells JavaScript to convert binary to a number containing the decimal representation of 101010.
If binary is not a string, it will be converted to one using the toString() function.

let x = '101010';

parseInt(x, 2)

The toString() method also handles non-integers and negative numbers. For example:

x = -101010
parseInt(x, 2); 

x = 101010.101010;
parseInt(x, 2);

No Technology Method

How do you quickly convert 101010 to 42 without a computer?
It takes some practice to make it easy, but here’s a few ways to convert a binary string to a decimal number.
One method discussed is doubling, described below:

Take the binary string.
Starting from the left, double your previous total and add the current digit.
Double your current total and add the next leftmost digit.
Repeat the previous step until you have gone through the entire string.

Below is a JavaScript function that implements the above procedure:

function toDecimal(v) {
  let binary = '';
  if(typeof v == 'string') {
    binary = v.split();
  } else {
      binary = v.toString().split();
  }
  let decimal = 0;
  for(let i = 0; i < binary.length; i++) {
      decimal = (decimal * 2) + binary[i];
  }
  return decimal;
}