findSumEvenNumbersRange()

Step 1: Understand the Problem and Initialize the Function

Before you start to code, it's crucial to understand what the question asks. In this case, we need to create a function, findSumEvenNumbersRange, that sums all of the even numbers within a certain range.

function findSumEvenNumbersRange(start, end) {}

Step 2: Initialize a Variable for the Sum

Inside the function, we'll create a variable to hold our sum. Let's call this variable 'sum'. Initially, sum would be zero as we haven't started adding any numbers yet.

function findSumEvenNumbersRange(start, end) {
    var sum = 0;
}

Step 3: Use a Loop to Go Through Each Number in the Range

Next, we'll use a for loop to iterate (or "go through") each number between start and end, inclusive. We'll start at 'start', go until we reach 'end', and increase by 1 each time through the loop.

function findSumEvenNumbersRange(start, end) {
    var sum = 0;
    for(var i=start; i <= end; i++) {}
}

Step 4: Conditionally Add Even Numbers to Our Sum

We only want to sum up the even numbers. To check if a number is even, we can use the modulus operator (%). This operation gives us the remainder after division. If we divide a number by 2 and the remainder is 0, that means the number is evenly divisible by 2, and hence, it's even. If 'i' is even, we add it to our 'sum'.

function findSumEvenNumbersRange(start, end) {
    var sum = 0;
    for(var i=start; i <= end; i++) {
        if(i % 2 === 0) {
            sum += i;
        }
    }
}

Step 5: Return the Sum

Lastly, we need to return the final sum. This will be the output of our function.

function findSumEvenNumbersRange(start, end) {
    var sum = 0;
    for(var i=start; i <= end; i++) {
        if(i % 2 === 0) {
            sum += i;
        }
    }
    return sum;
}

And voila! You've just created a JavaScript function that sums up all the even numbers in a given range. This function traverses the range once, making it an O(n) operation where n is the size of the range. Efficient and easy to read!

Remember: Programming is all about breaking down larger problems into smaller, more manageable parts. Take each step one at a time, and you'll have your problem solved in no time!