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to Binary in the JavaScript Track

Published at Jul 13 2018 · 0 comments
Test suite


This solution was written on an old version of Exercism. The tests below might not correspond to the solution code, and the exercise may have changed since this code was written.

Convert a binary number, represented as a string (e.g. '101010'), to its decimal equivalent using first principles.

Implement binary to decimal conversion. Given a binary input string, your program should produce a decimal output. The program should handle invalid inputs.


  • Implement the conversion yourself. Do not use something else to perform the conversion for you.

About Binary (Base-2)

Decimal is a base-10 system.

A number 23 in base 10 notation can be understood as a linear combination of powers of 10:

  • The rightmost digit gets multiplied by 10^0 = 1
  • The next number gets multiplied by 10^1 = 10
  • ...
  • The nth number gets multiplied by 10^(n-1).
  • All these values are summed.

So: 23 => 2*10^1 + 3*10^0 => 2*10 + 3*1 = 23 base 10

Binary is similar, but uses powers of 2 rather than powers of 10.

So: 101 => 1*2^2 + 0*2^1 + 1*2^0 => 1*4 + 0*2 + 1*1 => 4 + 1 => 5 base 10.


Go through the setup instructions for JavaScript to install the necessary dependencies:


Running the test suite

The provided test suite uses Jasmine. You can install it by opening a terminal window and running the following command:

npm install -g jasmine

Run the test suite from the exercise directory with:

jasmine binary.spec.js

In many test suites all but the first test have been marked "pending". Once you get a test passing, activate the next one by changing xit to it.


All of Computer Science http://www.wolframalpha.com/input/?i=binary&a=*C.binary-_*MathWorld-

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.


var Binary = require('./binary');

describe('binary', function () {
  it('0 is decimal 0', function () {
    expect(new Binary('0').toDecimal()).toEqual(0);

  xit('1 is decimal 1', function () {
    expect(new Binary('1').toDecimal()).toEqual(1);

  xit('10 is decimal 2', function () {
    expect(new Binary('10').toDecimal()).toEqual(2);

  xit('11 is decimal 3', function () {
    expect(new Binary('11').toDecimal()).toEqual(3);

  xit('100 is decimal 4', function () {
    expect(new Binary('100').toDecimal()).toEqual(4);

  xit('1001 is decimal 9', function () {
    expect(new Binary('1001').toDecimal()).toEqual(9);

  xit('11010 is decimal 26', function () {
    expect(new Binary('11010').toDecimal()).toEqual(26);

  xit('10001101000 is decimal 1128', function () {
    expect(new Binary('10001101000').toDecimal()).toEqual(1128);

  xit('00011111 is decimal 31', function () {
    expect(new Binary('00011111').toDecimal()).toEqual(31);

  xit('invalid inputs are decimal 0', function () {
    expect(new Binary('carrot').toDecimal()).toEqual(0);
    expect(new Binary('012').toDecimal()).toEqual(0);
    expect(new Binary('10nope').toDecimal()).toEqual(0);
    expect(new Binary('nope10').toDecimal()).toEqual(0);
    expect(new Binary('10nope10').toDecimal()).toEqual(0);
function Binary(string){
    this.toDecimal = function() {
	return string.split('').reverse().reduce(function(decimal,x,index){
		return (x==1) ? (decimal + Math.pow(2,index)) : decimal ;


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