When you return nothing from the reduce function it returns undefined and undefined + 1 === NaN. You should instead filter the array before reducing.
records.filter(({gender}) => gender === 'BOYS')
.reduce((sum, record) => sum + record.value)
When you return nothing from the reduce function it returns undefined and undefined + 1 === NaN. You should instead filter the array before reducing.
records.filter(({gender}) => gender === 'BOYS')
.reduce((sum, record) => sum + record.value)