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);

Commencez par l’exemple TypeScript Playground lié et l’affectation this.maybeNum = Math.max(this.maybeNum) dans la classe JavaScript. Suivez l’effet de cette affectation sur l’appel ultérieur takesString(this.maybeNum), puis vérifiez la correction avec le type attendu number | null ou un diagnostic noImplicitAny.