JavaScript reduce throwing error for more than two items

Question

I have this array:

const arr = [
  { someProp: [{ amount: 10 }]},
  { someProp: [{ amount: 12 }]},
];

and then this reduce fn:

con         


        

Answer 1

Following @Pointy answer, this is how you can get it working with any number of elements:

const sum = arr.reduce((prev, curr) => prev + curr.someProp[0].amount, 0);

prev is always the previously returned element, so you can safely use it as a number (and since you're just summing it, you can use 0 as default, so the first time reduce is invoked the value of prev will be 0)