comprehensive

Lightweight (1KB gzipped) Python-inspired object (dictionary) comprehension for JavaScript via template literals.

Overview

comprehensive provides a syntax for object comprehension in Javascript similar to Python's dictionary comprehension.

import toObj from 'comprehensive';
const people = [{name: 'Aidan', age: 20}, {name: 'Becca', age: 21}];

const ages = toObj`{person.name: person.age for person of ${people}}`;
// {Aidan: 20, Becca: 21}

or

const ages = toObj`{it.name: it.age over ${people}}`;

or

// Arbitrary transformations can be applied to the keys and/or values
const ages = toObj`${p => p.name}: ${p => p.age} over ${people}`

You can automatically unpack values from fixed-size nested arrays, which is particularly useful for iterating over another object.

const people = {
    ABC: {name: 'Aidan', age: 20},
    DEF: {name: 'Becca', age: 21}
}

const idMap = toObj`{id: person.name for id, person of ${Object.entries(people)}}`
// { ABC: 'Aidan', DEF: 'Becca' }

Or, you can iterate over the keys of an object using the for key in construct.

const places = {
    Toronto: {population: 2809000}, 
    Montreal: {population: 1714000}
}
toObj`{city: ${city => places[city].population} for city in ${places}`
// {Toronto: 2809000, Montreal: 1714000}

This is a shorthand for for city of ${Object.keys(places)}.

Installation

$ npm install comprehensive

You can also include dist/comprehensive.min.js in your project.

Usage

Basic syntax is as follows:

toObj`{k: v for var1, (var2, ...) of ${someArray}}`
toObj`{k: v over ${someArray}}`
toObj`{k: v for key in ${someObject}}`

where k and v can either be a property path (e.g. a.b.c), a function (e.g. ${a => a.b.c.toLowerCase()}), or a static value (e.g. ${123}). The key must either be a string or a number, otherwise toObj will throw. It will also throw if the syntax is invalid.

If you want to ensure the call never throws, you can use toObjSafe, which will return null on invalid input.

Note that toObj does not require curly brackets, and extra whitespace is allowed.

Examples

Basic Example

import toObj from 'comprehensive';
const people = [{name: 'Aidan', age: 20}, {name: 'Becca', age: 21}];

const personLookup = toObj`{p.name: p for p of ${people}}`;
// {Aidan: {name: Aidan, age: 20}, Becca: {name: 'Becca', age: 21}}

over syntax

const squares = toObj`{it: ${it => it ** 2} over ${[1, 2, 3, 4, 5]}}`;
// { '1': 1, '2': 4, '3': 9, '4': 16, '5': 25 }

Static Values

const obj = toObj`it: ${{hello: 'world'}} over ${'A,B,C'.split(',')}`;
// {A: {hello: 'world'}, B: {hello: 'world'}, C: {hello: 'world'}}

Mapped Key

const people = [{name: 'Daniel', hobby: 'Karate'}];

toObj`${p => `${p.name}-san`}: p for p of ${people}`;
// {'Daniel-san': {name: 'Daniel', hobby: 'Karate'}}

Iterate Over Object

const movie2Id = {'Shrek': 'tt0126029', 'Shrek 2': 'tt0298148'};
const id2Movie = toObj`{id: title for title, id of ${Object.entries(movie2Id)}}`;
// {tt0126029: 'Shrek', tt0298148: 'Shrek 2'}

or

const id2Movie = toObj`{${title => movie2Id[title]}: title for title in ${movie2Id}}}`;
// {tt0126029: 'Shrek', tt0298148: 'Shrek 2'}

or

const id2Movie = toObj`{${title => movie2Id[title]}: title for title of ${Object.keys(movie2Id)}}}`;
// {tt0126029: 'Shrek', tt0298148: 'Shrek 2'}

Nested Object Comprehensions

const provinces = [
    {
        province: 'Ontario',
        cities: [{city: 'Toronto', population: 2809000}]
    },
    {
        province: 'Quebec',
        cities: [{city: 'Montreal', population: 1714000}]
    }
];

const populations = toObj`{
    p.province : ${p => toObj`{c.city: c.population for c of ${p.cities}}`} for p of ${provinces}
}`;
// { Ontario: { Toronto: 2809000 }, Quebec: { Montreal: 1714000 }