typescript-error v0.1.3

typescript-error

Provides Rust-like Result and Option objects for Typescript.

Installation

Install using npm.

npm install --save typescript-error

Usage

Result\<T, E>

Use Result<T, E> as a return value for functions or methods that might error. This provides a way to indicate errors in a type-safe manner, analogous to a throws Exception in other languages like Java.

import { * } from "typescript-error"

class ParseException extends Error {}
class Integer {
  constructor(public value: number) {}
}

function parse(text: string): Result<Integer, ParseException> {
  let num = parseInt(text);
  if (isNaN(num)) {
    return Err(new ParseException("Text does not represent a number"));
  }
  else {
    return Ok(new Integer(num));
  }
}

let userInput = "15";
let result = parse(userInput);

if (!result.hasError()) {
  let intValue = result.unwrap();
  // Do something...
}
else {
  let error = result.getError();
  // Do something with error
}

Calling Result#unwrap() on a value that contains an error will throw the error, so you should only call it if you know that your result doesn't have an error. In development, it can be useful to call unwrap() without checking it first, for sake of brevity, or because you would want your script to choke on a failure there.

A common pattern for code that doesn't want to deal with an exception is to have a return type of Result, and just return the error-containing result (or call Err() on the exception itself).

Option\

Use Option<T> for functions or methods that may or may not return a value (such as getters), rather than returning null. This ensures that consuming code has to be aware of and explicitely deal with the fact that your method may not return a value:

import { * } from "typescript-error"

class ExampleJSON {
  private values: {[name: string]: string} = {};
  constructor() {}
  
  public getValue(key: string): Option<string> {
    if (key in this.values) {
      return new Some(this.values[key]);
    }
    else {
      return new None();
    }
  }
}

let json = new ExampleJSON();
let key = "Dawn Summers";
let value = json.getValue(key);

if (value instanceof Some) {
  print `${key} is the key to ${key.getValue()}`;
}
else {
  print `No value associated with the following key: "${key}"`;
}