My solution for Mysterious Organism

mysterious-organism.js

// Returns a random DNA base
const returnRandBase = () => {
  const dnaBases = ['A', 'T', 'C', 'G']
  return dnaBases[Math.floor(Math.random() * 4)] 
}

// Returns a random single stand of DNA containing 15 bases
const mockUpStrand = () => {
  const newStrand = []
  for (let i = 0; i < 15; i++) {
    newStrand.push(returnRandBase())
  }
  return newStrand
}

const pAequorFactory = (number, array) =>{
  return {
    specimenNum: number,

    dna: array,

    //Change some bases of the DNA
    mutate (){
      const randomNum = Math.floor(Math.random() * array.length);
      let randomBase = returnRandBase();
      if (this.dna[randomNum] === randomBase){
        let randomBase = returnRandBase();
        this.dna[randomNum] = randomBase;
      } else {
        this.dna[randomNum] = randomBase;
      }
      return this.dna;
    },

    //Compare two instances
    compareDNA (pAequor){
      let commonDNA = 0;
      let j = 0;

      for (dna in this.dna){
        if (this.dna[dna] === pAequor.dna[j]){
          commonDNA ++;
        }
        j ++;
      }


      const percentage = ((commonDNA/this.dna.length) * 100).toFixed();
      
      return `specimen #${this.specimenNum} and specimen #${pAequor.specimenNum} have ${percentage}% DNA in common`
    },
  
    //Method for the chance of survival
    willLikelySurvive (){
      let timesOfGOrC = 0;
      for (dna in this.dna){
        if (this.dna[dna] === "G" || this.dna[dna] === "C"){
          timesOfGOrC ++;
        }
      }

      const percentage = (timesOfGOrC/(this.dna.length)*100).toFixed();

      if (percentage >= 60){
        return true;
      } else {
        return false;
      }
    },

    //Complementary DNA strand
    complementStrand (){
      for (base in this.dna){
        if (this.dna[base] === "A"){
          this.dna[base] = "T";
        } else if (this.dna[base] === "G"){
          this.dna[base] = "C";
        } else if (this.dna[base] === "T"){
          this.dna[base] = "A";
        } else if (this.dna[base] === "C"){
          this.dna[base] = "G";
        } 
      }
      return this.dna; 
    }
  }   
};

//Creating 30 instances
let i = 1;
let arrayOfSurvive = [];
while (i < 31){
  let instance = pAequorFactory(i, mockUpStrand());
  if (instance.willLikelySurvive() === true){
    arrayOfSurvive.push(instance)
  }
  i ++;
}

//Check the survive instances
console.log(arrayOfSurvive);



//Check the complementStrand

/*let complementStrandProof = pAequorFactory(1, mockUpStrand());
console.log(complementStrandProof.dna);
console.log(complementStrandProof.complementStrand())
*/