JavaScript class property becomes `any` without warning when used in a function that is assigned to itself

🔎 Search Terms

jsdoc class null any

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about any

⏯ Playground Link

https://www.typescriptlang.org/play?strictNullChecks=true&useDefineForClassFields=true&filetype=js#code/KYDwDg9gTgLgBAYwDYEMDOa4DEITgbwCg4S4B6AKguNLgrgAEwUoUBbAgOwFc2AjYFAD8AXzhsUATwEA5XjVIUyCxBE5oYUbghjQAFBOnA5bAJQEVtGAAsAlmgB0h2bzgBeODyRIA3IUukNvYOaMAwALJSLmx6pn60Iv60oRFRxryxFrRWdo7O6RwekTZOKCB6QXlpJnEqiSqU1Nn0TCzsBBpQtpwA5mKdlkoqMCgA1sBoAMqa3T16neb49bQAZriZRNmBuQ4j41MzvRU7+TXxW+RkF9cAenf3D-cAtC9PnniCUNAANOLVrvY4ChOJI6oREkA

💻 Code

export class Foo {
    /**
     * @param {number?} maybeNum
     */
    constructor(maybeNum) {
        this.maybeNum = null;

        this.setMaybeNum();
    }

    setMaybeNum() {
        this.maybeNum = Math.max(this.maybeNum);
    }

    /**
     * @param {string} str
     */
    takesString(str) {}

    foo() {
        this.takesString(this.maybeNum);
        //               ^^^^^^^^^^^^^---- no error, maybeNum is any
    }
}

🙁 Actual behavior

this.maybeNum is any

🙂 Expected behavior

this.maybeNum is number | null or (since noImplicitAny is set) an error is emitted warning the user that this.maybeNum is any.

Additional information about the issue

It seems like the core issue here is this line:

this.maybeNum = Math.max(this.maybeNum);

Beginnen Sie mit dem verknüpften TypeScript Playground-Beispiel und der Zuweisung this.maybeNum = Math.max(this.maybeNum) in der JavaScript-Klasse. Verfolgen Sie, wie sich diese Zuweisung auf den späteren Aufruf takesString(this.maybeNum) auswirkt, und überprüfen Sie anschließend die Korrektur anhand des erwarteten Typs number | null oder einer noImplicitAny-Diagnose.