Item 83: Don't Consider Migration Complete Until You Enable noImplicitAny

要点

• Don't consider your TypeScript migration done until you adopt noImplicitAny. Loose type checking can mask real mistakes in type declarations.
• Fix type errors gradually before enforcing noImplicitAny. Give your team a chance to get comfortable with TypeScript before adopting stricter checks.

正文

class Chart {
  indices: any

  // ...
}

💻 playground

---

class Chart {
  indices: number[]

  // ...
}

💻 playground

---

getRanges() {
  for (const r of this.indices) {
    const low = r[0];
    //    ^? const low: any
    const high = r[1];
    //    ^? const high: any
    // ...
  }
}

💻 playground

---

getRanges() {
  for (const r of this.indices) {
    const low = r[0];
    //          ~~~~ Element implicitly has an 'any' type because
    //               type 'Number' has no index signature
    const high = r[1];
    //           ~~~~ Element implicitly has an 'any' type because
    //                type 'Number' has no index signature
    // ...
  }
}

💻 playground