I'm recreating Javascript's map function and i'm not understanding where these parameters are coming from:

(this[index], index, this)

I understand what this is the array, i understand this[index] is the value, and index is the number that keeps track of the index on iteration, but where is that all coming from when i'm only passing in:

x => x * 5

that's the part i'm confused about and havne't found a good explanation about it online.

Array.prototype.mymap = function(callback) {
    const resultArray = [];
    for (let index = 0; index < this.length; index++) {
        resultArray.push(callback(this[index], index, this));  // confused about these parameters
    }
    return resultArray;
}

const sample = [1,2,3];    
var output = sample.mymap(x => x * 5);    
console.log(output);