Useful TypeScript defaults.

default.tsconfig.json

{
  // Note: This assumes TS6+.
  "compilerOptions": {
    // Treat all files as ES modules.
    "moduleDetection": "force",

    // For Node.js:
    // "module": "nodenext",
    // "types": ["node"],

    // In arr: string[], arr[0] correctly becomes 'string | undefined'
    // instead of incorrect 'string'.
    "noUncheckedIndexedAccess": true,
    // Non-empty switch cases without return/break/throw (implicit fallthrough) will error.
    "noFallthroughCasesInSwitch": true,
    // Require explicit 'override' keyword in front of overriding class methods.
    "noImplicitOverride": true,
    // Require importing and exporting types with the explicit 'type' keyword prefix.
    "verbatimModuleSyntax": true,
    
    // Force explicitly returning a value (instead of implicitly returning undefined)
    // for all code paths if a function doesn't return void (already returns a value for some code paths).
    "noImplicitReturns": true,
    // obj: { optional?: string } will error when explicitly setting obj.optional = undefined
    // (it would otherwise create inconsistent behavior for 'x in y' checks).
    "exactOptionalPropertyTypes": true,
    // Force explicit indexed access (instead of dot access) for generic index signature properties
    // (eg. obj: { [key: string]: string } would have to be accessed using obj['prop'] instead of obj.prop).
    "noPropertyAccessFromIndexSignature": true,

    // Disallow enums, namespaces and modules with runtime code, parameter properties in classes,
    // and some legacy syntax (the <prefix>-style type assertions syntax and CommonJS import/export assignments).
    "erasableSyntaxOnly": true,

    // Don't type check any declaration (.d.ts) files, gaining performance and convenience at the cost of
    // losing type safety at the library boundary (relying on library authors to maintain accurate declarations).
    "skipLibCheck": true
  }
}