I am learning javascript and Ive stumbled upon issue that I do not understand. Could somebody explain to me why in method compareDNA I need to use parentheses while using this.dna and in the previous method it works just fine?
// 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;
};
function pAequorFactory(specimenNum, dna){
return {
specimenNum,
dna,
mutate(){
let i = Math.floor(Math.random() * 15)
let newGene = returnRandBase()
while (this.dna[i] === newGene){
newGene = returnRandBase()
}
this.dna[i] = newGene
return this.dna
},
compareDNA(object){
let counter = 0
for(let i = 0; i < this.dna().length; i++){
if(this.dna()[i] === object.dna()[i]){
counter++
}
}
let percentage = counter / this.dna().length * 100
return `Specimen number ${this.specimenNum} and specimen number ${object.specimenNum} have ${percentage}% of DNA in common.`
},
}
}
let aligator = pAequorFactory(1, mockUpStrand)
let dog = pAequorFactory(2, mockUpStrand)
console.log(aligator.compareDNA(dog))
console.log(dog.dna().length)The problem is that the dna that is passed as an argument is a function, so it becomes a method of the returned object, and needs to be called with .dna(). However, this looks like a mistake - actually an array should have been passed:
let aligator = pAequorFactory(1, mockUpStrand())
// ^^
let dog = pAequorFactory(2, mockUpStrand())
// ^^
Then you can access .dna[i] or .dna.length as normal.
If you don't do that, dog.dna() returns a different DNA every time, which doesn't make sense.
using
this.dnaand in the previous method it works just fine?
Actually, it doesn't. dog.mutate() does return a function with a single integer property. It's supposed to return an array really.