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Destructuring and optional properties on an interface #4647
Description
Hi,
I am trying to perform a destructuring assignment in a method signature using a variable that is declared as an interface that has an optional property. I'm getting an error when specifying multiple levels of defaults.
Please take a look at the following code. I expected test number 3 to compile cleanly, but it gives an error. Tests 2 and 5 give what I think is an appropriate error. The rest compile cleanly.
For test 3, since a default is provided for B, I don't think it should be considered mandatory.
This is with TypeScript 1.6 beta. Please let me know if I'm doing something wrong.
Thanks, team!
-Steve O
interface AB {
A: string;
B?: string;
}
const childObject: AB = {
A: "test"
}
const parentObject = {
childObject
};
function function1({childObject: {A, B = ""}}) {
console.log(A);
console.log(B);
}
function function2({childObject: {A, B = ""} = {A: "", B: ""}}) {
console.log(A);
console.log(B);
}
function function3({childObject: {A, B} = {A: "", B: ""}}) {
console.log(A);
console.log(B);
}
/* Test #1: Compiles cleanly */
function1(parentObject);
/*
Test #2: Gives expected error.
Error: Argument of type '{}' is not assignable to parameter of type '{ childObject: { A: any; B?: string; }; }'. Property 'childObject' is missing in type '{}'.
*/
function1({});
/*
Test #3: Not sure why this one is giving an error. A default is provided for B if the object exists, so
technically B is not required. I would have only expected to see this error on Test #5 below.
Argument of type '{ childObject: AB; }' is not assignable to parameter of type '{ childObject?: { A: string; B: string; }; }'. Types of property 'childObject' are incompatible. Type 'AB' is not assignable to type '{ A: string; B: string; }'.
Property 'B' is optional in type 'AB' but required in type '{ A: string; B: string; }'.
*/
function2(parentObject);
/* Test #4: Compiles cleanly */
function2({});
/*
Test #5: Gives expected error. (Same as #3 but this one makes sense.)
Argument of type '{ childObject: AB; }' is not assignable to parameter of type '{ childObject?: { A: string; B: string; }; }'. Types of property 'childObject' are incompatible. Type 'AB' is not assignable to type '{ A: string; B: string; }'.
Property 'B' is optional in type 'AB' but required in type '{ A: string; B: string; }'.
*/
function3(parentObject);
/* Test #6: Compiles cleanly */
function3({});
Activity
nycdotnet commentedon Sep 4, 2015
By the way - using this code on babeljs.io logs "test" and "b1" which is what I would have expected from test number 3 above. Also, the TypeScript code works as expected - it's just the type error that I'm concerned with.
danquirk commentedon Sep 4, 2015
This #4598 will fix your issue.
nycdotnet commentedon Sep 4, 2015
Thanks.