Function evaluate

html.js:18–71

(h, built, fields, args)

const PROP_APPEND = MODE_PROP_APPEND;

const evaluate = (h, built, fields, args) => {
	let tmp;

	// `build()` used the first element of the operation list as
	// temporary workspace. Now that `build()` is done we can use
	// that space to track whether the current element is "dynamic"
	// (i.e. it or any of its descendants depend on dynamic values).
	built[0] = 0;

	for (let i = 1; i < built.length; i++) {
		const type = built[i++];

		// Set `built[0]`'s appropriate bits if this element depends on a dynamic value.
		const value = built[i] ? ((built[0] |= type ? 1 : 2), fields[built[i++]]) : built[++i];

		if (type === TAG_SET) {
			args[0] = value;
		}
		else if (type === PROPS_ASSIGN) {
			args[1] = Object.assign(args[1] || {}, value);
		}
		else if (type === PROP_SET) {
			(args[1] = args[1] || {})[built[++i]] = value;
		}
		else if (type === PROP_APPEND) {
			args[1][built[++i]] += (value + '');
		}
		else if (type) { // type === CHILD_RECURSE
			// Set the operation list (including the staticness bits) as
			// `this` for the `h` call.
			tmp = h.apply(value, evaluate(h, value, fields, ['', null]));
			args.push(tmp);

			if (value[0]) {
				// Set the 2nd lowest bit it the child element is dynamic.
				built[0] |= 2;
			}
			else {
				// Rewrite the operation list in-place if the child element is static.
				// The currently evaluated piece `CHILD_RECURSE, 0, [...]` becomes
				// `CHILD_APPEND, 0, tmp`.
				// Essentially the operation list gets optimized for potential future
				// re-evaluations.
				built[i-2] = CHILD_APPEND;
				built[i] = tmp;
			}
		}
		else { // type === CHILD_APPEND
			args.push(value);
		}
	}

	return args;
};

const build = function(statics) {