Calculate sum of elements in an array within a function

I'm doing a prework for a course I'm going to attend and I have to complete some ex. I started learning JS last week so I'm a newbie and in this ex I don't have to use any method that allows me to calculate the sum. I only have to use logic. (for loops-functions-switch)

This is the ex: Define a function that will receive an array as an argument and calculate a sum of all its elements. For example, if we pass the following array to that function: const prices = [5, 7.99, 9.99, 0.99, 21], it should return 44.97 as output. How would you concatenate $ sign in front of the sum?

I don't really know how to do that sum, in fact the code I've written is totally wrong but I'd like to understand the logic behind.

function calculator (someArray) {
  let result;
  for(let i=0; i<= someArray.length; i++) {
    console.log(someArray[i]);
  }
  result=someArray[i] + someArray[i+=1];
}

const prices = [5, 7.99, 9.99, 0.99, 21];

calculator(prices);

I've now changed the code but it only prints the first 2 elements of the array:

function calculator (someArray) {
  let result;
  for(let i = 0; i<= someArray.length; i++) {
    result = someArray[i] + (someArray[i+=1]);
    console.log(result);
    return result;
  }
}

const prices = [5, 7.99, 9.99, 0.99, 21];

calculator(prices);

Solution

This is the ex: Define a function that will receive an array as an argument and calculate a sum of all its elements. For example, if we pass the following array to that function: const prices = [5, 7.99, 9.99, 0.99, 21], it should return 44.97 as output. How would you concatenate $ sign in front of the sum?

Javascript has a nice feature: reduce

function calculator (someArray){
  return someArray.reduce((howMuchSoFar,currentElementOfTheArray) => {
    howMuchSoFar = howMuchSoFar + currentElementOfTheArray;
    return howMuchSoFar;
  });
}

const prices = [5, 7.99, 9.99, 0.99, 21];

console.log("$"+calculator(prices));

(intentionally verbose)

Going back to your original code (a classic for loop)

arrays go from 0 to length-1, control that
whathever[i+=1] is actually doing two things: i=i+1 and bringing whatever[i] , it is better going step by step for now, and inside the loop you're already doing i++ so this won't be good
return is for the whole function, not for each step of a classic for. If needed, go with break, but please understand firstly the while loop

function calculator (someArray){
  let result=0;
  for( let i = 0; i< someArray.length; i++){  
    result = result + someArray[i];
  }
  return result;
}

const prices = [5, 7.99, 9.99, 0.99, 21];

console.log("$"+calculator(prices));