for example:
interface A {
a: number
}
interface B {
a: number
b: string
}
const X = (x) => {
//
return x
}parameter x may be An or B.
if type An is passed in, you want to check that x is returned after the operation, and if you have the attribute b, it is an error.
if type B is passed in, you want to check that x is returned after the operation, and it is an error without attribute b.
you want to return the type of x, and the assertion is equal to the type passed in.
A handwritten overload can be done
ts ts
:
interface A {
a: any
}
interface B {
a: any
b: any
}
function isB(arg: A | B): arg is B {
return (<B>arg).b !== undefined;
}
function foo(arg: A | B) {
if (isB(arg)) {
// arg is B
console.log(arg.a, arg.b)
} else {
// arg is A
console.log(arg.a)
}
}
if I understand it wrong, ignore it, the big god spurts
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