snq

snq (Safe Navigation Query)

snq is a utility function to safely navigate arrays and object properties without getting type errors. It is not an original idea at all and is actually adapted and only slightly different from idx. The main differences are as follows:

• snq returns undefined whenever a TypeError happens, regardless of the reason for the error and throws an error only if it is not a TypeError. idx returns null, if the cause of the error is a null value and throws an error if the error is not caused by an undefined or null value.
• snq has an optional second parameter which works as default value to return instead of undefined.
• idx requires the source object as a first parameter. snq does not.
• idx has a Babel plugin for replacing idx instances with conventional traversing in order to improve performance. Although it is not benchmarked yet, due to lack of reason checks, it is safe to say that snq is faster than idx. Thus, a Babel plugin could prove insignificant for snq.
• snq is written in TypeScript and, unlike idx, it does not support Flow types.

When optional chaining operator finally lands, libraries like snq and idx may become redundant.

Installation

Run the following code in your terminal:

yarn add snq

or if you are using npm:

npm install --save snq

Setup

import snq from 'snq';

Usage

Consider the following interfaces as products list:

interface Price {
  amount: number;
  currency: string;
  symbol?: string;
}

interface Product {
  id: number;
  name: string;
  inStock: boolean; 
  price?: {
    final: Price;
    original?: Price;
  };
}

This is how it would probably look like when you want to get original price symbol of first product:

products.length &&
products[0].price &&
products[0].price.original &&
products[0].price.original.symbol

Otherwise, you will get a type error. Using snq, it is safe to write the following:

const symbol = snq(() => this.products[0].price.original.symbol);

// symbol is undefined if a type error happens, actual value if not

There is an optional second argument which represents the default value to return when a type error happens.

const symbol = snq(() => this.products[0].price.original.symbol, '$');

// symbol is "$" if a type error happens, actual value if not

The type of the symbol returned will be inferred as string in both cases.

Check the demo application out.