newbie js learner , pls help

Question

this code returns NaN , I´m missing something, and I don´t know what. Help please.
function calculateMass(freightItems) {
let totalMass = 0;
totalMass = freightItems.reduce((accum,sum) => accum.lenght + sum.length , totalMass);

return totalMass;
}

const mass = calculateMass(['dog', 'donkey', 'cat']);
console.log('Total mass of items is ' + mass); // should be 12

Answer 1

Try:
freightItems.forEac(el=>totalMass+=el.length);

Sorry, but I didn't use reduce. I will look for what is it and bring new reply maybe.

Answer 2

It means Not a Number, as far as I know, but that doesnt really help me much

Answer 3

Nowdays was add NaN as infinity, but it is like a "error".

Commom appear when divided by 0, and can't divide by 0, then NaN.