preact/src/h.js

1-h-overview.js

import { VNode } from './vnode';
import options from './options';

// a single empty array shared among all child-less nodes to prevent having to allocate one array each
const EMPTY_CHILDREN = [];

export function h(nodeName, attributes) {
	let children = // deleted code to calculate children
	let p = new VNode(nodeName, attributes || undefined, children || EMPTY_CHILDREN);

	// if a "vnode hook" is defined, pass every created VNode to it
	if (options.vnode) options.vnode(p);

	return p;
}

2-calculate-children.js

// stack of children or arrays of children left to process
const stack = [];

let children, lastSimple, child, simple, i;

// Children can be passed as extra arguments to `h`
for (i=arguments.length; i-- > 2; ) {
	stack.push(arguments[i]);
}
// They can also be passed in the `attributes` parameter, but should not be used as actual html attributes
if (attributes && attributes.children) {
	if (!stack.length) stack.push(attributes.children);
	delete attributes.children;
}
// Loop until we have flattened and normalized all children
while (stack.length) {
	// if the stack item is an array, just push all its elements onto the stack
	if ((child = stack.pop()) instanceof Array) {
		for (i=child.length; i--; ) stack.push(child[i]);
	}
	// Now with each individual child, coerce it to something we can render:
	else if (child!=null && child!==true && child!==false) {
		if (typeof child=='number') child = String(child);
		simple = typeof child=='string';
		if (simple && lastSimple) {
			children[children.length-1] += child;
		}
		else {
			(children || (children = [])).push(child);
			lastSimple = simple;
		}
	}
}