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Lecture 1: How to Start a Startup by Y Combinator, genius.com This text is annotated! Click on the highlights to read what others are saying. If you'd like to add your own insights, comments, or questions to specific parts of the lecture, visit the lecture page on Genius, highlight the relevant text, and click the button that pops up. Your annotation will appear both here and on Genius.

Welcome to CS183B. I am Sam Altman, I'm the President of Y Combinator. Nine years ago, I was a Stanford student, and then I dropped out to start a company and then I've been an investor for the last few. So YC, we've been teaching people how to start startups for nine years. Most of it's pretty specific to the startups but thirty percent of it is pretty generally applicable. And so we think we can teach that thirty percent in this class. And even though that's only thirty percent of the way there, hopefully it will still be really helpful.

We've taught a lot of this class at YC and it's all been off the record. And this is

I’m going to hold the unpopular on SO selenium tag opinion that XPath is preferable to CSS in the longer run.

This long post has two sections - first I'll put a back-of-the-napkin proof the performance difference between the two is 0.1-0.3 milliseconds (yes; that's 100 microseconds), and then I'll share my opinion why XPath is more powerful.

Performance difference

Let's first tackle "the elephant in the room" – that xpath is slower than css.

Please include a repro

How to create a minimal reproduction

Create a sample repo on GitHub
Demonstrate the problem, and nothing but the problem. If the app where you're experiencing the issue happens to use Gulp, I don't care, unless the problem involves Gulp. Remove that stuff. Whittle it down to the bare minimum of code that reliably demonstrates the issue. Get rid of any dependencies that aren't directly related to the problem.
Install all your dependencies to package.json. If I can't clone the repo and do npm install && npm run build (or similar – see point 4) to see the problem, because I need some globally installed CLI tool or whatever, then it's not really a minimal reproduction.
Include instructions in the repo, along with a description of the expected and actual behaviour. Obviously the issue should include information about the bug as well, but it's really helpful if README.md

	export function assertEventType<
	TE extends EventObject,
	TType extends TE['type']
	>(event: TE, eventType: TType): asserts event is TE & { type: TType } {
	if (event.type !== eventType) {
	throw new Error(
	`Invalid event: expected "${eventType}", got "${event.type}"`,
	)
	}
	}

	My Awesome Sketch
	First State
	some event -> Second State
	Second State

	import { copyStream } from '../common/messages'

	type Unarray<T> = T extends Array<infer R> ? R : T;
	type Unobservable<T> = T extends Observable<infer R> ? R : T;
	type Unpacked<T> = T extends Array<infer R> ? R : T extends Observable<infer R> ? R : never;

	type CopyData = Unobservable<typeof copyStream>
	type BackgroundEvent =
	\| { type: 'copy'; data: CopyData }
	\| { type: 'xstate.done.performCopy'; data: { tabId: string } }

	const fs = require("fs");

	const filepath = "craco-changed-files.json";

	/**
	* This overwrites a log file of file changes that caused a rebuild.
	*/
	class ChangedFilesLogPlugin {
	constructor() {
	fs.writeFileSync(filepath, JSON.stringify([], null, 2), "utf8");

	/**
	* Use this in testing to control when a promise resolves
	*/
	function defer<T>() {
	let resolve: (value?: T) => void
	let reject: (error: any) => void
	const promise = new Promise<T>((res, rej) => {
	resolve = res
	reject = rej
	})

	# Eliminates inline script from index.html
	INLINE_RUNTIME_CHUNK=false