FAQ: Learn TDD With Mocha - Red to Green II

This community-built FAQ covers the “Red to Green II” exercise from the lesson “Learn TDD With Mocha”.

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This exercise can be found in the following Codecademy content:

Web Development

Learn JavaScript Unit Testing

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Is it typical to use ‘for’ loops over array methods in professional software development or was that just used as an example for this exercise.

I answered my own question as I got to the next step in this lesson

As an alternative, I was looking through Stack Overflow and we could do this:

const Calculate = {
	sum(inputArray) {
		const reducer = (accumulator, currentValue) => accumulator + currentValue;
		const sum = inputArray.reduce(reducer);
		return sum;
	}
}

1 Like

Yes it’s nice, even more concise you can just return :

return inputArray.reduce((acc, currV) => acc + currV); 

Happy coding ! :slight_smile:

3 Likes

Two easy ways of doing this:

sum(inputArray) {

    let totalSum = 0;

    inputArray.forEach((element) => totalSum += element)

    return totalSum;
  }

or…

sum(inputArray) {

    const result = inputArray.reduce((accumulator, currentValue) => accumulator + currentValue);

    return result;
  }
1 Like

It won’t me pass with this one:

const Calculate = {
	sum(inputArray) {
    const reducer = (previousValue, currentValue) => previousValue + currentValue;
    return inputArray.reduce(reducer)
	}
}

module.exports = Calculate;

I used this code, which I’ve tested in the terminal and elsewhere, which does work:

const Calculate = {
	sum(inputArray) {
		const result = inputArray.reduce((a, b) => {
      return a + b;
    })
    return result;
	}
}

It seems the exercise wants us to specifically use a for…of loop instead of e.g. an array.reduce() method, but this isn’t specified anywhere, so that a little unhelpful when the code still works - surely the exercise’s pass condition should reflect the output of the tests we’re running?

I attempted to solve it using the reduce iterator, but I keep getting an error. I believe I’ve implemented it correctly so it might be a CodeAcademy issue.

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