The title says it all on this one, if you have an object like:
const ingredients = {
'apples': 3,
'oranges': 9,
'pears': 4
}
and you want to calculate the total number of items you have then you can do:
const sum = Object.keys(ingredients)
.map(ingredientKey => {
// get an array of numbers
return ingredients[ingredientKey];
})
.reduce((sum, el) => {
// sum that array of numbers
return sum + el;
}, 0);