带有 Class 的 Typescript 泛型不起作用或我做错了什么？

Question

class Some<AttributeType = {
    bar: string
}> {
    foo(attrs: AttributeType) {
        if (attrs.bar) {
            console.log(attrs.bar)
        }
    }
}

ts failed with error

Property 'bar' does not exist on type 'AttributeType'.

https://www.typescriptlang.org/play?#code/FAYwNghgzlAEDKB7AtgUwDwEEAu2BOAlgEYCu2qAKgJ4AOqsAvLAN7CzuxER4BcsU+AgDsA5sAC+APhZsOAM0SIAFBFx4ofHINLlqdAJQyOx2ATmwVaqADoueQ6xNPYIREKiIwqa2EQjL+DZ2+rJO4qGw4eFAA

Answer 1

Use extends keyword instead of = :

class Some<AttributeType extends {  bar: string  }>

More here ( TypeScript generic constraints ).

By using the = syntax you provided a default generic parameter and you can use your class in a following way:

let x: Some;

Which would be impossible if you removed it. What you need is to define a constraint which will allow the compiler to infer that your generic type always contains bar field.