api/sample/dev/talk/bundle/mithril-2.2.2/render/hyperscriptVnode.js

"use strict"

var Vnode = require("./vnode")

// Call via `hyperscriptVnode.apply(startOffset, arguments)`
//
// The reason I do it this way, forwarding the arguments and passing the start
// offset in `this`, is so I don't have to create a temporary array in a
// performance-critical path.
//
// In native ES6, I'd instead add a final `...args` parameter to the
// `hyperscript` and `fragment` factories and define this as
// `hyperscriptVnode(...args)`, since modern engines do optimize that away. But
// ES5 (what Mithril.js requires thanks to IE support) doesn't give me that luxury,
// and engines aren't nearly intelligent enough to do either of these:
//
// 1. Elide the allocation for `[].slice.call(arguments, 1)` when it's passed to
//    another function only to be indexed.
// 2. Elide an `arguments` allocation when it's passed to any function other
//    than `Function.prototype.apply` or `Reflect.apply`.
//
// In ES6, it'd probably look closer to this (I'd need to profile it, though):
// module.exports = function(attrs, ...children) {
//     if (attrs == null || typeof attrs === "object" && attrs.tag == null && !Array.isArray(attrs)) {
//         if (children.length === 1 && Array.isArray(children[0])) children = children[0]
//     } else {
//         children = children.length === 0 && Array.isArray(attrs) ? attrs : [attrs, ...children]
//         attrs = undefined
//     }
//
//     if (attrs == null) attrs = {}
//     return Vnode("", attrs.key, attrs, children)
// }
module.exports = function() {
	var attrs = arguments[this], start = this + 1, children

	if (attrs == null) {
		attrs = {}
	} else if (typeof attrs !== "object" || attrs.tag != null || Array.isArray(attrs)) {
		attrs = {}
		start = this
	}

	if (arguments.length === start + 1) {
		children = arguments[start]
		if (!Array.isArray(children)) children = [children]
	} else {
		children = []
		while (start < arguments.length) children.push(arguments[start++])
	}

	return Vnode("", attrs.key, attrs, children)
}