Getting started with Result

Convert this:

import { existsSync, readFileSync } from 'fs';

function readFile(path: string): string {
    if (existsSync(path)) {
        return readFileSync(path);
    } else {
        // Callers of readFile have no way of knowing the function can fail
        throw new Error('invalid path');
    }
}

// This line may fail unexpectedly without warnings from typescript
const text = readFile('test.txt');

To this:

import { existsSync, readFileSync } from 'fs';
import { Ok, Err, Result } from 'ts-results-es';

function readFile(path: string): Result<string, 'invalid path'> {
    if (existsSync(path)) {
        return new Ok(readFileSync(path)); // new is optional here
    } else {
        return new Err('invalid path'); // new is optional here
    }
}

// Typescript now forces you to check whether you have a valid result at compile time.
const result = readFile('test.txt');
if (result.isOk()) {
    // text contains the file's content
    const text = result.value;
} else {
    // err equals 'invalid path'
    const err = result.error;
}