Dates are output as strings in ISO format

[arion-p]

It is impossible to output any Date data to Excel. exceljs expects date data to be Javascript Date object to output them properly so that Excel can handle them. However, after fixing #137 all dates are passed to exceljs as strings (in ISO format). The reason is that JSON.parse(JSON.stringify(vm)) doesn't make an exact deep copy. JSON.stringify(vm) turns dates in ISO formatted strings but JSON.parse(....) does not turn them back to Date objects. It rather leaves them as strings.

We either need the proxy solution or a proper deep copy.

[Siemienik]

Thank you for open this issue, I will look on it soon.

[arion-p]

A reviver function could be used in JSON.parse to turn ISO date strings back to Dates but it is hard to identify which ones are really dates and which are strings. Creating a map of Date properties in the source before JSON.stringify might help but I'm not sure how it could be used from the reviver function (it only gets a key which is local to the object being parsed). Another option would be to also use a replacer function in JSON.stringify to turn Dates to composite objects with some discriminator property that the reviver can identify.

[Siemienik]

Great ideas, I will definitely check them out. So far, I was considering another cloning function, the one using JSON is primitive, which your example demonstrates perfectly. By the way, contributions to this project are very welcome, so feel free to submit a PR 😃

I'm planning to tackle this issue soon. Currently, along with several contributors from exceljs, we are trying to clear the PR list (currently at 70 PRs 🙈 ). We coordinate on Discord: https://discord.gg/BqTQGHDKw8. I mention this because this project is based on exceljs, so working there brings double benefits :D