Boris Cherny’s Blog

• Do you treat derived data and non-derived data the same?
• Should users interact with the two the same way?
• Do you re-compute dependent data in a lazy or eager way?
• How much control do you need over re-computing derived

type Props = {
href?: string
onClick?: () => void
text: string
}

function Button(props: Props) {
if ('href' in props) {
return (
<a className="Button" href={props.href}>
{props.text}
</a>
)
}
if ('onClick' in props) {
return (
<button className="Button" onClick={props.onClick}>
{props.text}
</button>
)
}
throw ReferenceError('You must pass either href or onClick to <Button />')
}

let a = <Button text="Click me" href="https://github.com" />
let b = <Button text="Click me" onClick={() => {}} />

// OK. Should be an error
let c = <Button text="Click me" href="https://github.com" onClick={() => {}} />

// OK. Throws an error at runtime
let d = <Button text="Click me" />

• Exceptions bubble up through the call tree
• State has to be lifted up to the root of a call tree
• If a function is async, its ancestors must be too
• Centralized services also centralize any decentralized services that call them
• In a physical system, if you know the position and momentum of an object A and it collides with

• fetch, XMLHTTPRequest, etc. (REST)
• Swagger (REST)
• Falcor (REST)
• Apollo (GraphQL)
• Relay (GraphQL)
• Protobuf

• Investing (long term). Investing for the long term is all about holding a diverse set of assets for as long as possible. It doesn’t matter if you invest at discounted

# when I ran ESM TypeScript code the wrong way:
Error [ERR_REQUIRE_ESM]: Must use import to load ES Module

# when I imported an ESModule from a CommonJS .js file:
Error [ERR_REQUIRE_ESM]: require() of ES Module .../lodash.js from .../index.cjs not supported

# when I imported an ESModule from a .ts file:
error TS1479: The current file is a CommonJS module whose imports will produce 'require' calls

# when I used ES6 import syntax in a .js file:
SyntaxError: Cannot use import statement outside a module