I am trying to correctly code my chainable function in Typescript. Below is the code
const sum = (val: number | undefined) => {
let internal = Number(val);
if (val) {
return function sumup(_val: number | undefined) {
if (_val && internal !== undefined) {
internal += _val;
return sumup;
}
return internal;
};
}
return internal;
};
console.log('sum:', sum(1)(2)(3)());
The function is working to the point that I get the correct result. However, it is yielding a typescript error: This expression is not callable. Not all constituents of type 'number | ((_val: number | undefined) => number | ...)' are callable. Type 'number' has no call signatures.
How would I correctly code such a sum function without using class or this?
You can achieve this by describing precisely the functions behaviors with function overloads:
function sum(): number
function sum(val: number): typeof sum
function sum(val?: number): number | typeof sum {
let internal = Number(val);
if (val) {
function sumup(): number
function sumup(_val: number): typeof sumup
function sumup(_val?: number): number | typeof sumup {
if (_val && internal !== undefined) {
internal += _val;
return sumup;
}
return internal;
};
return sumup;
}
return internal;
};
console.log('sum:', sum(1)(2)(3)());