I'm currently learning JavaScript and was trying to test the limitations of the Spread Operator along with the reduce() method.
Example:
const numArray = [1, 6, 9, 4, 21, 8, 15];
const sumEvenOdd = numArray.reduce((acc, current) =>
current % 2 === 0
? {...acc,'even': acc.even + current}
: {...acc,'odd': acc.odd + current},
{"even": 0, "odd": 0}
);
console.log(sumEvenOdd); //{ even: 18, odd: 46 }
As you could see from the above code, I was able to mutate the initial value of the reduce() method which is an object: {"even": 0, "odd": 0} to track the sum of the even and odd numbers of numArray and use the Spread Operator to fill-in the other remaining property.
Question:
Can I do the same thing if I have an array of objects as the initial value? e.g., [{"even": 0}, {"odd": 0}] and if not, what can I do as an alternative so I could fill-in the other properties that I didn't mention like for example if the objects also contain other properties? e.g., [{"even": 0, "color": ""...}, {"odd": 0, "color": ""...}]
yes, you can modify array with any props
you can use any type for reduce: objects, arrays, numbers, strings, boolean
A few examples with different types:
const concatNumbersAsString = [0,1,2].reduce((a,c) => a + c, '');
const flatNestedArrays = [[0],[1],[2]].reduce((a,c) => a.concat(c), [])
const checkBoolCondition = [0,1,2].reduce((a,c) => [1].includes(c), true)
const calculateSum = [0,1,2].reduce((a,c) => a + c, 0)
console.log('concatNumbersAsString', concatNumbersAsString)
console.log('flatNestedArrays', flatNestedArrays)
console.log('checkBoolCondition', checkBoolCondition)
console.log('calculateSum', calculateSum)Modifying an array:
const numArray = [1, 6, 9, 4, 21, 8, 15];
const sumEvenOdd = numArray.reduce((acc, current) =>
current % 2 === 0
? acc.map(i => i.hasOwnProperty('even') ? {...i, even: i.even + current} : i)
: acc.map(i => i.hasOwnProperty('odd') ? {...i, odd: i.odd + current} : i),
[{"even": 0, color: 'red'},{ "odd": 0, color: 'green'}]
);
console.log(sumEvenOdd)