fix error on reduce and reduceRight doc

[junpos]

1. on first iteration amount is undefined which results in NaN for total.

it('reduce', function () {
  const total = wrapper.find(Bar).reduce((amount, n) => {
    console.log(amount, n.prop('amount'));
    return amount + n.prop('amount');
  });
  expect(total).to.equal(16);
});

AssertionError: expected NaN to equal 16
  + expected - actual

    -NaN
    +16

// log
undefined 2
NaN 4
NaN 8

It needs a sanity check whether amount is defined, or have an initial value.

wrapper.find(Bar).reduce((acc, n) => {
  const amount = n.prop('amount');
  return acc 
    ? acc + amount
    : amount;
});
//or
wrapper.find(Bar).reduce((amount, n) => amount + n.prop('amount'), 0);

2. And the total should be 14 instead of 16

[ljharb]

actually, on the first iteration amount is the first item - that's the behavior of reduce when omitting the initial value.

[ljharb]

in other words, [1, 2, 3].reduce(function (prev, item) { console.log([prev, item]); }); logs [1, 2] and then [undefined, 3]

[ljharb]

If enzyme's reduce fails to have the same behavior as Array#reduce, that's a bug we need to fix.

[ljharb]

I've put up #673 to fix this bug, thanks for the PR!

[nfcampos]

@ljharb since we have #673 shouldn't this one be closed?

[ljharb]

@nfcampos good call