In Simple Words, it reduces the given array to a single value.

The reduce() method executes a reducer function (that you provide) on each element of the array, resulting single output value.

Syntax :

 yourArray.reduce(callback, initialValue)

Here ,

• yourArray : the array to run the reducer function on.

• Callback : Reducer Function

• initialValue (optional ): it's the initial value of the accumulator, if it is not provided it is the default value of the array's first element.

Example without initialValue :

const Numbers = [2,3,1,4,5,6];
const reducer = (accumulator, currentValue) => {
        console.log(`Accumulator :  ${accumulator}`);
        console.log(`Current Array Element : ${currentValue}`);
        return accumulator + currentValue;
};

const sum = Numbers.reduce(reducer);
console.log(`Sum is ${sum}.`);

/*
 Accumulator : 2
Current Array Element : 3
Accumulator : 5;
Current Array Element : 1
Accumulator : 6
Current Array Element : 4
Accumulator : 10
Current Array Element : 5
Accumulator : 15
Current Array Element : 6;
Sum is 21.
*/

Example with initialValue :

const Numbers = [2,3,1,4,5,6];
const reducer = (accumulator, currentValue) => {
        console.log(`Accumulator :  ${accumulator}`);
        console.log(`Current Array Element : ${currentValue}`);
        return accumulator + currentValue;
};

const sum = Numbers.reduce(reducer,0);
console.log(`Sum is ${sum}.`);

/*
 Accumulator : 0
Current Array Element : 2
Accumulator : 2;
Current Array Element : 3
Accumulator : 5
Current Array Element : 1
Accumulator : 6
Current Array Element : 4
Accumulator : 10
Current Array Element : 5;
Accumulator : 15
Current Array Element : 6 
Sum is 21.
*/

Here is the basic and better examples to understand reduce() function easily.

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