I have used declaration merging as follows
function barfoo(): void { /* magic */ }
namespace barfoo {
export let maz: Array<string> = [];
}
But the question is, how can I use this. For example, if I use it as follows
function doIt(cb: barfoo): void {
cb.maz = [10];
cb();
}
typescript is complaining: Cannot find name 'barfoo'.
Any suggestions how to fix the type (without using any :) ?
UPDATE: I figured out how to create new functions of this type
let x: { (): Array<string>; maz: Array<string>; };
x = (() => {
var _x : any = function () { };
_x.maz = [];
return _x;
})();
let y: { (): void; maz: Array<string> } = (() => {
let _y: any = function fake(): Array<string> {
return ((cb: any): Array<string> => {
return cb.maz;
})(fake);
}
_y.maz = [];
return _y;
})();
But, as you can see, the second example is very complex. Is this the correct way or can this be simplified?
Your problem is that barfoo is a value, but in your definition of doIt() you are mistakenly treating it as a type. All values have a type, but the name of a value is rarely the name of its type. If I do let x = 3; then x is a value, but its type is number, not x.
It seems from your code you want to be able to pass in the value barfoo to the function. (Why you would want to do such a thing is your business, but if you're only ever going to pass that one value into the function, you might want to consider not having it be a parameter at all. Up to you, though.) So the cb parameter should be declared to be the type of barfoo, whatever it is. By inspection you can see it is something like { (): void; maz: string[] }. But luckily TypeScript allows you to quickly get the type of a named value by using a type query, which reuses the keyword typeof. The type of barfoo is simply typeof barfoo:
function doIt(cb: typeof barfoo): void {
cb.maz = [10]; // error, hey 10 is not a string
cb();
}
This works, and even catches another bug for you. Hope that helps; good luck!
If you want to make more objects of the same type as barfoo, that is: a callable function (of no arguments and returning void) which also has a maz property containing an array of strings, the most straightforward way to do it is to use Object.assign(), which merges all properties into the first argument and returns it as the intersection of all the argument types. Like this:
const barfoo2 = Object.assign(
function() {
// function body here
},
{maz: ["some","stuff"]}
);
doIt(barfoo2); // works
Good luck again!
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