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to Rna Transcription (Legacy) in the JavaScript Track

Test suite

RNA Transcription

Given a DNA strand, return its RNA complement (per RNA transcription).

Both DNA and RNA strands are a sequence of nucleotides.

The four nucleotides found in DNA are adenine (A), cytosine (C), guanine (G) and thymine (T).

The four nucleotides found in RNA are adenine (A), cytosine (C), guanine (G) and uracil (U).

Given a DNA strand, its transcribed RNA strand is formed by replacing each nucleotide with its complement:

  • G -> C
  • C -> G
  • T -> A
  • A -> U


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 rna-transcription.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.


Rosalind http://rosalind.info/problems/rna

Submitting Incomplete Solutions

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


var DnaTranscriber = require('./rna-transcription');
var dnaTranscriber = new DnaTranscriber();

describe('toRna()', function () {
  it('transcribes cytosine to guanine', function () {

  xit('transcribes guanine to cytosine', function () {

  xit('transcribes adenine to uracil', function () {

  xit('transcribes thymine to adenine', function () {

  xit('transcribes all dna nucleotides to their rna complements', function () {

  xit('correctly handles completely invalid input', function () {
    expect(function () { dnaTranscriber.toRna('XXX'); }).toThrow(
      new Error('Invalid input')

  xit('correctly handles partially invalid input', function () {
    expect(function () { dnaTranscriber.toRna('ACGTXXXCTTAA'); }).toThrow(
      new Error('Invalid input')
module.exports = 

class DnaTranscriber {
  toRna(s) {
    const nucleotides = { G: 'C', C: 'G', T: 'A', A: 'U'}
    return Array.from(s).map(n => {
      if (n in nucleotides)
        return nucleotides[n]
      throw new Error('Invalid input')

What can you learn from this solution?

A huge amount can be learnt from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that I could read more about to develop my understanding?