Overloading TypeScript functions with Observable<T | T[]>

Looking for some guidance from the experts: Is there a way to simplify the function overload in the example below by removing as Observable<string[]> and using T and T[] instead?

Here's a basic example to illustrate:

import { Observable } from 'rxjs';

class Test<T> {
    test(flag : string) : Observable<T>;
    test(flag : string) : Observable<T[]>;
    test(flag : string) : Observable<T | T[]>
    {
        if (flag === 'foo')
        {
            return new Observable<T>();
        }
        return new Observable<T[]>();
    }
}

const test : Test<string | string[]> = new Test();

test.test('foo');

(test.test('bar') as Observable<string[]>).subscribe(foo => foo.map(bar => bar));

Now, let's explore a real-world Angular scenario:

import { Injectable } from '@angular/core';
import { Observable } from 'rxjs';
import { OptionWithBodyInterface } from './common.interface';
import { CommonService } from './common.service';
import { MethodType } from './common.type';
import { createUrl } from './helper';

@Injectable()
export class RequestService<T> extends CommonService
{
    public request(method : MethodType, options? : OptionWithBodyInterface) : Observable<T | T[]>
    {
        return this.http.request<T | T[]>(method, createUrl(this.getApiUrl(), this.getEndpoint()),
        {
            ...this.getOptions(),
            ...options
        });
    }
}

Answer №1

Here is the solution I crafted:

import { Injectable } from '@angular/core';
import { Observable } from 'rxjs';
import { OptionsWithBody } from '../common';
import { CommonService } from '../common';
import { Method } from '../common';
import { createUrl } from '../common';

@Injectable()
export class RequestService<T> extends CommonService
{

    public request<$ = T | T[]>(method : Method, options ?: OptionsWithBody) : Observable<$>
    {
        return this.http.request<$>(method, createUrl(this.getApiUrl(), this.getApiRoute()),
        {
            ...this.getOptions(),
            ...options
        });
    }
}

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