Fix IE11 not setting initial select value

[marvinhagemeister]

Oh boy, it took me all day to figure this one out. Basically all browsers will infer the option value from textContent when it isn't present. It's probably done for backwards compatibility.

const option = document.createElement("option");
option.textContent = "A";
console.log(option.value); // Logs: "A"

At this point option.value is set and that will skip our own check later:

preact/src/diff/index.js

Line 248 in c2909d0

if (('value' in newProps) && newProps.value!==undefined && newProps.value !== dom.value) dom.value = newProps.value==null ? '' : newProps.value;

This works fine in all browsers except IE11. When the option value isn't explicitly set, it leads to subtle bugs like select.value not working anymore. In this case it will always reset it to an empty string 🤷‍♂️

@andrewiggins this is basically a continuation from #1708 and it turns out that my fix wasn't correct. This PR gets those bytes back 😉

Here is a simple test case to verify the behavior in IE11:

// IE11 Bug: <select> value won't be set correctly
var select = document.createElement("select");
var data = ["A", "B", "C"];
for (var i = 0; i < data.length; i++) {
	var option = document.createElement("option");
	option.textContent = data[i];
	// Uncomment this line to make `select.value` work
	// option.value = data[i];
	select.appendChild(option);
}

document.body.appendChild(select);
select.value = "C";
console.log("actual:", select.value, "expected: C");
// Logs: actual: "" expected: C

Removes -24 B 🎉

[coveralls]

Coverage increased (+0.4%) to 99.875% when pulling 39d2a1f on IE11-select into c2909d0 on master.

[cristianbote]

WOW! Absolutely mental work! 🎉🎊

[JoviDeCroock]

Wow, nice one! 💯

[developit]

this is the best PR I have ever seen