Why this code returns 10 instead of 2?
var arrToSum = [2, 4, 10];
function sumArray(array) {
var result = 0;
for (var i = array[0]; i < array.length; i++) {
result += array[i];
}
return result;
}
sumArray(arrToSum);
// function returns 10
If following loop logic, I would end after adding 2 to result variable, because next i is equal to 3 and loop should end. Please explain what happens there.
How things are working in for loop:
for (var i = array[0]; i < array.length; i++) {
In the loop, these are the results after execution of first Iteration;
First Iteration; i = 2
var i = array[0]; // i = 2;
result += array[i]; // result = 10;
array[i] is array[2] which is 10. Hence, the result is 10.
Second Iteration; i = 3
array.length is 3 since it has 3 elements. Condition i < array.length; is false and code Breaks out of loop, returning the Result as 10.
You are starting from 2 (value of array[0]), not from 0. Change
for (var i = array[0]; i < array.length; i++) {
to
for (var i = 0; i < array.length; i++) {
This is why you should familiarize yourself with functional programming in javascript. map, filter, reduce are your friends. Especially map.
Try to avoid regular loops as much as possible cause they are more error prone. In your case you've messed up with counter variable i.
var sum = [2, 4, 10].reduce((a, b) => a + b, 0);
iruns from2to2, effectively only addingarr[2](10) to0. It's not clear to me what you are intending withvar i = array[0];. To expand a bit: "because nextiis equal to3" Yes, you are adding only a single value, the loop stops after a single iteration, but sinceistarts at2you are addingarr[2], notarr[0]. Btw, if you want to understand what exactly your code is doing, set a breakpoint, step through your code step by step and inspect the variables.array[2]is 10