966e78bcab
* Implement support for variadic arguments to `m.fragment` While I was at it, I refactored the common logic out of `hyperscript`. * Add a missed change from #2326 * Update docs + changelog [skip ci] * Explain rationale for `hyperscriptVnode`'s calling convention This way, it doesn't get erroneously "cleaned up" into something worse, and so it's clearer how it'd be potentially optimized once ES5 support is dropped.
53 lines
2 KiB
JavaScript
53 lines
2 KiB
JavaScript
"use strict"
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var Vnode = require("../render/vnode")
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// Call via `hyperscriptVnode.apply(startOffset, arguments)`
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//
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// The reason I do it this way, forwarding the arguments and passing the start
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// offset in `this`, is so I don't have to create a temporary array in a
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// performance-critical path.
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//
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// In native ES6, I'd instead add a final `...args` parameter to the
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// `hyperscript` and `fragment` factories and define this as
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// `hyperscriptVnode(...args)`, since modern engines do optimize that away. But
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// ES5 (what Mithril requires thanks to IE support) doesn't give me that luxury,
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// and engines aren't nearly intelligent enough to do either of these:
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//
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// 1. Elide the allocation for `[].slice.call(arguments, 1)` when it's passed to
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// another function only to be indexed.
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// 2. Elide an `arguments` allocation when it's passed to any function other
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// than `Function.prototype.apply` or `Reflect.apply`.
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//
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// In ES6, it'd probably look closer to this (I'd need to profile it, though):
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// module.exports = function(attrs, ...children) {
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// if (attrs == null || typeof attrs === "object" && attrs.tag == null && !Array.isArray(attrs)) {
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// if (children.length === 1 && Array.isArray(children[0])) children = children[0]
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// } else {
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// children = children.length === 0 && Array.isArray(attrs) ? attrs : [attrs, ...children]
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// attrs = undefined
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// }
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//
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// if (attrs == null) attrs = {}
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// return Vnode("", attrs.key, attrs, children)
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// }
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module.exports = function() {
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var attrs = arguments[this], start = this + 1, children
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if (attrs == null) {
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attrs = {}
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} else if (typeof attrs !== "object" || attrs.tag != null || Array.isArray(attrs)) {
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attrs = {}
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start = this
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}
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if (arguments.length === start + 1) {
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children = arguments[start]
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if (!Array.isArray(children)) children = [children]
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} else {
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children = []
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while (start < arguments.length) children.push(arguments[start++])
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}
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return Vnode("", attrs.key, attrs, children)
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}
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