TypeScript Version: 2.4.0
Code
interface A {
a: string;
b: string;
}
// A
const a0: A = {
a: "a",
b: "b",
c: "c", // (1)
};
// B
const b1 = {
a: "a",
b: "b",
c: "c", // (4)
};
const a1: A = { ...b1 /* (2) */ };
// C
interface B {
a: string;
b: string;
c: string; // (5)
}
const b2: B = {
a: "a",
b: "b",
c: "c",
};
const a2: A = { ...b2 /* (3) */ };Expected behavior:
Type incompatible error at c: "c", // (1), ...b1 /* (2) */ and ...b2 /* (3) */
Type '{ a: string; b: string; c: string; }' is not assignable to type 'A'.
Object literal may only specify known properties, and 'c' does not exist in type 'A'.
Actual behavior:
Error at c: "c", // (1), c: "c", // (4) and c: string; // (5). The later two are confusing.
I really don't know how can this check improve code quality. I can always assign the spread result to a temp local variable and then assign it to the final value, TypeScript doesn't care about this at all:
const b1 = {
a: "a",
b: "b",
c: "c",
};
const a1: A = b1; 
TypeScript Version: 2.4.0
Code
Expected behavior:
Type incompatible error at
c: "c", // (1),...b1 /* (2) */and...b2 /* (3) */Actual behavior:
Error at
c: "c", // (1),c: "c", // (4)andc: string; // (5). The later two are confusing.I really don't know how can this check improve code quality. I can always assign the spread result to a temp local variable and then assign it to the final value, TypeScript doesn't care about this at all: