那么如何将来自 react redux 的数组中所有对象的所有值相加？

Question

This is react redux reducer file where numbers array is:

const initialState = {
numbers: [ { name: 'max', num: 3 }, { name: 'jack', num: 2 } ]
}

This is how I want to sum all the num values in all objects in numbers array which is recieved from react redux state reducer file

In component:

    useEffect(() => {
        const total = props.numbers.reduce((prev, current) => {
            return prev + current.num, 0;
        });
        console.log(total);
        console.log(props.numbers);
    }, []);

This is the console logs from useEffect:

0

(2) [{…}, {…}]
0: {name: "max", num: 3}
1: {name: "jack", num: 2}
length: 2
__proto__: Array(0)

The total const is just 0 and its not working.

So how can I sum all the num values in all objects in an array which is coming from redux reducer file??

Answer 1

The , 0 should be the second argument to reduce , not in the return :

const total = props.numbers.reduce((prev, current) => {
  return prev + current.num;
}, 0);

Answer 2

you need to fix reduce:

const total = props.numbers.reduce((prev, current) => {
     return prev + current.num;
}, 0);

Answer 3

You can also use map function

sum = 0;
props.numbers.map(n => {
    sum+= n.num;
})

Answer 4

You need to provide an initial value for prev , as the second param of reduce . If its not provided then during the first run, first param of callback function is the first element of array and second param of callback function is the second element of array. Then the return value is passed to the first param and the next element is the second value.

So, to add I have added 0 as the initial value.

 const numbers = [ { name: 'max', num: 3 }, { name: 'jack', num: 2 } ] const total = numbers.reduce((prev, { num }) => { return prev + num }, 0) console.log(total)