Bug Report

On JavaScript type checking (checkJs option), object initializer with function property ({ foo: function () {} }) emits ts2339 error unexpectedly, if that function gets and sets other properties of this.

🔎 Search Terms

checkJs function method definitions

🕗 Version & Regression Information

• v3 (at least v3.9.7 on playground) does not emit an error. v4 emits an error,

⏯ Playground Link

https://www.typescriptlang.org/play?declaration=false&useJavaScript=true#code/MYewdgzgLgBAHjAvDA3gKBpmBDAXDABgBoMsAjfY0zAMwFcxgoBLcAZQE8wps597GLcDAAUASlTUsmKAAtmEAHTYkMAIwBuKdNCQQAGwCmi-SADmIuQsVkxGmAHoHMAAoAnEAAdDbqBxgA5GQBMAAmIIYQMGAgsIZwCrDCft6BAkysYJzcvAGKIgBMAMxFAJxiUgC+JNIAtoZyIKHZPHDiktLSVkoqyJraWLoQBsamFt02dlU1WOlCWVytAOrMjXRQAIIQEMxmYPXc-AwZwu3onYPgw0Ym5pbySrZa0pVolRpAA

💻 Code

// @ts-check
const x = {
    a: 0,
    b: 0,
    functionSyntax: function () {
        this.a = 1;
        console.log(this.b); // Property 'b' does not exist on type 'functionSyntax'.(2339)
    },
    methodSyntax() {
        this.a = 1;
        console.log(this.b); // no error
    },
    functionSyntaxWithoutAssignment: function () {
        console.log(this.b); // no error
    }
};

🙁 Actual behavior

ts(2339) error Property '{name}' does not exist on type '{function name}'. is reported

🙂 Expected behavior

No error

The method declaration syntax ({ foo() {} }) does not emit an error. I think that function syntax should have the same behavior for this checking.