Why wont it print an array of 15 letters?

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JavaScript

I'm trying to print an array of 15 elements to the console.
Currently it only prints something like ['G'] or ['A'].

I thought my splice code would work because splice works by basically saying:

(at this element number, replace this amount of elements, with this string)

so, see my splice formula below:

//this.DNA.splice(Math.floor(Math.random()*15), 1, returnRandBase());

Should surely translate to: (0 - 14, 1, A or T or C or G)

// 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
}

//factory function 
  const pAequorFactory = (specimenNum, DNA) => {
  return {
    specimenNum: specimenNum,
    DNA: DNA,

    //mutate takes in a 15 element array of DNA letters, picks a random element, and 
      changes
    //it's letter to something else. Letters are 'A', 'T', 'C', 'G'. It must not 
    //change it to the same letter.

    mutate(){
    let result =[];
    result = this.DNA.splice(Math.floor(Math.random()*15), 1, returnRandBase());
    return result;
    }
  }
};

var newObj = pAequorFactory(15, ['A', 'T', 'C', 'G', 'A', 'T', 'C', 'G', 'A', 'T', 'C', 'G', 'A', 'T', 'C']);

console.log(newObj.mutate());

What I have tried:

Nothing as it looks right to me so maybe someone can spot something

Posted 11-Jan-22 11:01am

Member 15496681

Updated 11-Jan-22 12:40pm

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Black Mamba Elapidae · Accepted Answer · 2022-01-11T12:40:00

Return this.DNA from mutate() instead of 'result'. Check splice documentation for more details... 'splice is a mutable function because it modifies the original array, while slice returns a new array'

// 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
}

//factory function 
  const pAequorFactory = (specimenNum, DNA) => {
  return {
    specimenNum: specimenNum,
    DNA: DNA,

    //mutate takes in a 15 element array of DNA letters, picks a random element, and changes
    //it's letter to something else. Letters are 'A', 'T', 'C', 'G'. It must not 
    //change it to the same letter.

    mutate(){
    let result =[];
    this.DNA.splice(Math.floor(Math.random()*15), 1, returnRandBase());
    return this.DNA;
    }
  }
};

var newObj = pAequorFactory(15, ['A', 'T', 'C', 'G', 'A', 'T', 'C', 'G', 'A', 'T', 'C', 'G', 'A', 'T', 'C']);

console.log(newObj.mutate());