Defining the first parameter for a function as an object which must have two keys both containing string values errors with a message: Duplicate identifier 'string'.
interface Func {
({value: string; error: string}, {other: number}): number;
}
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2 Answers
You've forgotten to add names for the parameters. The next code works for me:
interface Func
{
(param1: {value: string; error: string}, param2: {other: number}): number;
}
Comments
You need to name the parameters:
interface Func {
(firstParameter: {value: string; error: string}, secondParameter: {other: number}): number;
}
Interestingly not naming the second parameter is currently valid TypeScript code which allows you to pass any type of other that you want:
interface Func {
(firstParameter: {value: string; error: string}, {other: number}): number;
}
var func: Func = function({value: val, error: err}, {other: oth}) {
return 42;
};
// The type of the second parameter is `{other: any}` which allows you to pass
// a string instead of a number as you might think at a careless first glance:
func({value: 'value', error: 'snap'}, {other: 'bad'});
I am not yet sure what this interface is actually declaring.
Another confusing error message that can arise from not naming the first parameter is: ',' expected. if you have different types for the values, e.g.:
interface Func {
({value: string; error: boolean}, {other: number}): number;
}
@MarkDolbyrev's answer above is correct, I wanted to elaborate on it.