Mysterious organism challenge

[arc9323577458]

Hi, I am on the ‘Mysterious Organism’ challenge project. For step 4 I have written the code below in order to mutate a random letter in the DNA sequence. My thinking behind this was that if I create new variables with the potential letter replacements and then run through them to replace a randomly selected part of the 15 character array then that would work but I am receiving a syntax error and I can’t see why. The error is suggesting a ) is out of place. Please see code below and feel free to make any comments/suggestions.

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
}
//Factory function for organism

const pAequorFactory = (number , array) => {
  return obj = {
    specinum: number,
    dna: array,  
    mutate () {
      let ifA = ['T' , 'C' , 'G'];
      let ifT = ['A' , 'C' , 'G'];
      let ifC = ['A' , 'T' , 'G'];
      let ifG = ['A' , 'T' , 'C'];
     if (this.array[Math.floor(Math.random() * 15)] === 'A'){
       return ifA[Math.floor(Math.random() * 4)];
     }
    if (this.array[Math.floor(Math.random() * 15)] === 'T'){
       return ifT[Math.floor(Math.random() * 4)];
    }
    if (this.array[Math.floor(Math.random() * 15)] === 'C'){
       return ifC[Math.floor(Math.random() * 4)];
    }
    if (this.array[Math.floor(Math.random() * 15)] === 'G'){
       return ifG[Math.floor(Math.random() * 4)];
    }
    else {
        return 'Invalid number';
      }
    }
};

[arc9323577458]

Slight iteration on this:

const pAequorFactory = (number , array) => {
  return {
    specinum: number,
    dna: array,  
    mutate () {
      let ifA = ['T' , 'C' , 'G'];
      let ifT = ['A' , 'C' , 'G'];
      let ifC = ['A' , 'T' , 'G'];
      let ifG = ['A' , 'T' , 'C'];
      
      for (let i = 0; i < 15; i++){
      if (this.dna[i] === 'A'){
        this.dna[i] = ifA[Math.floor(Math.random() * 3)]
      }
      if (this.dna[i] === 'T'){
        this.dna[i] = ifT[Math.floor(Math.random() * 3)]
      }
      if (this.dna[i] === 'C'){
        this.dna[i] = ifC[Math.floor(Math.random() * 3)]
      }
      if (this.dna[i] === 'G'){
        this.dna[i] = ifG[Math.floor(Math.random() * 3)]
      }
      else {
        return 'Invalid'
      }
      console.log(this.dna);
      }
    }
  }
};