Javascript Reduce for object

January 3, 2023

const obj=[{
name: "john",
marks: 50
},
{
name: "mary",
marks: 55
},
{
name: "peter",
marks: 75
}
];

I want to calculate sum of marks using reduce method.

I tried through this way –

const sum = obj.reduce((next, number) => {
  console.log('next',next.marks);
  console.log('number',number.marks);
  return next.marks+ number.marks;
});    

console.log(sum);

But I am getting sum as NaN and overall result as –

next 50
number 55
next undefined
number 75
NaN

I am not sure why next is getting undefined in between.

How can I calculate sum through reduce method ?

>Solution :

Pass a default value to reduce as 0

const obj=[{ name: "john", marks: 50 }, { name: "mary", marks: 55 }, { name: "peter", marks: 75 } ];


const sum = obj.reduce((acc, number) => {
  return acc+ number.marks;
}, 0);

console.log(sum)