Roman Dvornov lahmatiy

Similar solutions with very different execution times. What's the reason? Why solution #1 is too slow?

Hint: access to .length property and to variables is not an issue.

Based on a real case in CSSTree

Node v6.11.3

N	Solution #1	Solution #2

	const csstree = require("css-tree");
	const cssDefinitions = ["color"];
	const ast = csstree.parse(`
	.some-selector {
	color: black;
	border: 1px solid #fff;
	}
	`, { parseValue: false });

	csstree.walk(ast, {

	const cssTree = require("[email protected]");

	function getSelectorParent(selector) {
	const selectorAst = cssTree.parse(selector, { context: 'selector' });

	// solution #1
	selectorAst.children.prevUntil(selectorAst.children.tail, (node, item, list) => {
	list.remove(item);
	return node.type === 'Combinator' \|\| node.type === 'WhiteSpace';
	});

	const cssTree = require("[email protected]");

	function getSelectorParent(selector) {
	const selectorAst = cssTree.parse(selector, { context: 'selector' });
	// solution #1
	// selectorAst.children.prevUntil(selectorAst.children.tail, (node, item, list) => {
	// list.remove(item);
	// return node.type === 'Combinator' \|\| node.type === 'WhiteSpace';
	// });

	const cssTree = require("[email protected]");

	function getSelectorParent(selector) {
	const selectorAst = cssTree.parse(selector, { context: 'selector' });
	// solution #1
	// selectorAst.children.prevUntil(selectorAst.children.tail, (node, item, list) => {
	// list.remove(item);
	// return node.type === 'Combinator' \|\| node.type === 'WhiteSpace';
	// });

	// UPDATE: you can use ready to use package prop-types-definition
	// https://github.com/avito-tech/prop-types-definition

	module.exports = function(content) {
	return content + `
	(function(ReactPropTypes) {
	function unwrapValueItem(value) {
	if (value) {
	if (typeof value.getTypeDefinition === 'function') {
	return value.getTypeDefinition();

	const csstree = require('css-tree');

	const ast1 = csstree.parse('.a { color: red }', {
	filename: './a.css',
	positions: true
	});
	const ast2 = csstree.parse('.b { color: red }', {
	filename: './b.css',
	positions: true
	});

	const csstree = require('css-tree');
	const data = require('mdn-data/css/properties.json');

	Object.keys(data).forEach(name => {
	const prop = data[name];

	if (Array.isArray(prop.initial)) {
	return;
	}

	const pngSignature = Buffer.from([137, 80, 78, 71, 13, 10, 26, 10]);
	const hashKey = 'react-snapshot-hash';
	const crcTable = [];
	const initialCrc = 0xffffffff;

	for (let n = 0; n < 256; n++) {
	let c = n;

	for (let k = 0; k < 8; k++) {
	if (c & 1) {

	const EXTENSION_TYPE = {
	0x01: 'PlainText',
	0xF9: 'GraphicControl',
	0xFE: 'Comment',
	0xFF: 'Application'
	};

	/**
	* Returns total length of data blocks sequence
	*