Javascript reduce with a nested array

Question

I'm trying to sum a nested array with the reduce method. My dat array looks like this:

var data = [
    [1389740400000, 576],
    [1389741300000, 608],
    [1389742200000, 624],
    [1389743100000, 672],
    [1389744000000, 691]
];

I got this:

// es5
data.reduce(function(prev, next) { return prev + next[1]; })

// es6 syntax
data.reduce((prev, next) => prev + next[1])

However I only do need the second value from each (nested) array. Any hints or tipps for me? I'm trying to sum all values within the array.

// Edit: Thanks for the answers. The problem was, that I missed the initialValue at the end.

// es6 solution
data.reduce((prev, next) => prev + next[1], 0)

Answer 1

Do it as following

var result = data.reduce(function (prev,next) {
    return prev + next[1];
},0);

console.log(result);//prints 3171

Here I am sending 0 as prev initially. So it will go like this

First Time  prev->0 next->[1389740400000, 576]
Second Time prev->576 next->[1389740400000, 608]

Do a console.log(prev,next) to understand much better.

If you'll see in docs you will get it.

Answer 2

A generic approach for all array, even if they are irregular styled.

Use: array.reduce(sum, 0)

function sum(r, a) {
    return Array.isArray(a) ? a.reduce(sum, r) : r + a;
}

console.log([
    [1389740400000, 576],
    [1389741300000, 608],
    [1389742200000, 624],
    [1389743100000, 672],
    [1389744000000, 691]
].reduce(sum, 0));

console.log([
    [1, 2, 3, 4],
    [5, 6, 7, 8],
    [9, 10, 11, 12, [13, 14, 15, 16]]
].reduce(sum, 0));