Starting observer only after DOM has loaded

[jakubfiala]

This PR makes it so the MutationObserver only kicks off if/after the DOM has fully loaded.

Rationale

This prevents issues when document.body isn't present for any reason. One might argue that it is the developer's responsibility to ensure that the code doesn't execute before body exists. I think it's better to account for that in the module itself.

Likely fixes #14

Implementation notes

Using DOMContentLoaded and checking for complete readystate because I'm assuming you don't support <IE10 anyway.

Using a higher-order function for the event handler for purity and the good of all humankind.

Checklist

• [x] tests: 19/19 passed
• [x] style: node node_modules/.bin/standard does not return any warnings

💥

[bcomnes]

I agree, this has been a problem for choo and nanocomponent in the past.

[bcomnes]

Looks like this was addressed at some point, but I like the code in this PR better, integrating.

[jakubfiala]

sweet, thanks @bcomnes