I've defined some functions in this object inside a function calculator because I want to chain them. My goal is to to overload the addNumber function but I can't seem to get the syntax right.
Below is an example of what I want to achieve (won't work because syntax is wrong)
const calculator = () => {
return {
result: 0,
addNumber(a: number) : number;
addNumber(a: number | b: number): number;
addNumber(a: number | b: string): number {
// Implementation to add numbers depending on function overload
return this;
},
multiplyNumber(a) {
this.result = this.result * a;
return this;
},
log() {
console.log(this.result);
}
};
}
// logs 10
calculator().addNumber(10).log();
// logs 25
calculator().addNumber(10,15).log();
// logs 25
calculator().addNumber(10,'15').log();
This is was the example that gave me the idea however, the function is defined normally. What are some ways I can overload a function that is defined in object?
function makeDate(timestamp: number): Date;
function makeDate(m: number, d: number, y: number): Date;
function makeDate(mOrTimestamp: number, d?: number, y?: number): Date {
if (d !== undefined && y !== undefined) {
return new Date(y, mOrTimestamp, d);
} else {
return new Date(mOrTimestamp);
}
}
const d1 = makeDate(12345678);
const d2 = makeDate(5, 5, 5);
const d3 = makeDate(1, 3);
If you are willing to switch to an anonymous class, then it's pretty simple to get overloading:
const calculator = () => {
return new class {
result = 0;
addNumber(a: number) : this
addNumber(a: number, b: number): this
addNumber(a: number, b: string): this
addNumber(a: number, b?: number | string): this {
// Implementation to add numbers depending on function overload
return this;
}
multiplyNumber(a: number) {
this.result = this.result * a;
return this;
}
log() {
console.log(this.result);
}
};
}
Object literal methods and function expressions don't support overloading. The only other option is to use a function expression with a type assertion:
const calculator = () => {
return {
result: 0,
addNumber : function (a: number, b?: number | string) {
return this;
} as {
<T>(this: T, a: number) : T
<T>(this: T, a: number, b: number): T
<T>(this: T, a: number, b: string): T
}
};
}