strat ·

strat is a modern, dependency-free TypeScript library for formatting strings in Deno and Node.js. It's inspired by Python's str.format() but is focused more on being at home in TypeScript than strictly adhering to Python's conventions.

If you want stricter Python conventions, check out string-format which served inspired the original version of this project.

features

• formatting can be partially applied, allowing for reusable template functions
• object property references with dot notation
• object methods are called and can be passed arguments
• TypeScript-friendly for Deno and Node.js

installation

deno

Import and use:

import { strat } from "jsr:@haltcase/strat";
import type { FormatPartial, Transformer /*...*/ } from "jsr:@haltcase/strat";

node

1. Install with your method of choice

   pnpm add strat
   npm install strat
   yarn add strat
   bun add strat

2. Import

   import { strat } from "strat";

usage

view from the top

const series = {
	title: "Arcane",
	seasons: 2,
	rottenTomatoesRating: 100,
};

strat("{title} ({rottenTomatoesRating}%) had {seasons} great seasons", series);
// -> "Arcane (100%) had 2 great seasons."

Compare that to the equivalent string concatenation in ES5:

series.title + " (" + series.rottenTomatoesRating + "%) had " + series.seasons +
	" great seasons.";

Or the more modern template literals from ES2015:

`${series.title} (${series.rottenTomatoesRating}%) had ${series.seasons} great seasons.`;

But the strat function can also be partially applied to create reusable template functions. Just leave out the initial replacements like so:

const template = strat(
	"{title} ({rottenTomatoesRating}%) had {seasons} great seasons",
);

template(madMen);
// -> "Mad Men (94%) had 7 great seasons."
template(haltAndCatchFire);
// -> "Halt and Catch Fire (90%) had 4 great seasons."
template(peakyBlinders);
// -> "Peaky Blinders (93%) had 6 great seasons."

partial application

When you omit the replacements, strat returns a partially applied, reusable instance.

import { strat } from "jsr:@haltcase/strat";
import { assertEquals } from "jsr:@std/assert/equals";

const result1 = strat("You got- you gotta run {}.", "Morty");
assertEquals(result1, "You got- you gotta run Morty.");

const result2 = strat("When you come to a {} in the road, {}.", [
	"fork",
	"take it",
]);
assertEquals(result2, "When you come to a fork in the road, take it.");

Here, the first argument is your template string. The second argument is an array of replacement values, or just a single value.

The second argument can optionally be left out, in which case a new function will be returned that you can call with your replacement parameters.

import { strat } from "jsr:@haltcase/strat";
import { assertEquals } from "jsr:@std/assert/equals";

const template = strat("Like {} and {}");

assertEquals(template(["salt", "pepper"]), "Like salt and pepper");

assertEquals(
	template(["peanut butter", "jelly"]),
	"Like peanut butter and jelly",
);

api

strat(template: string, replacements: any | [...values]): string

Returns the result of replacing each {…} placeholder in the template string with its corresponding replacement.

Placeholders may contain numbers which refer to positional arguments:

import { strat } from "jsr:@haltcase/strat";
import { assertEquals } from "jsr:@std/assert/equals";

assertEquals(
	strat("{0}, you have {1} unread message{2}", ["Holly", 2, "s"]),
	"Holly, you have 2 unread messages",
);

Unmatched placeholders produce no output:

import { strat } from "jsr:@haltcase/strat";
import { assertEquals } from "jsr:@std/assert/equals";

assertEquals(
	strat("{0}, you have {1} unread message{2}", ["Steve", 1]),
	"Steve, you have 1 unread message",
);

A format string may reference a positional argument multiple times:

import { strat } from "jsr:@haltcase/strat";
import { assertEquals } from "jsr:@std/assert/equals";

assertEquals(
	strat(`The name's {1}. {0} {1}.`, ["James", "Bond"]),
	"The name's Bond. James Bond.",
);

Positional arguments may be referenced implicitly:

import { strat } from "jsr:@haltcase/strat";
import { assertEquals } from "jsr:@std/assert/equals";

assertEquals(
	strat("{}, you have {} unread message{}", ["Steve", 1]),
	"Steve, you have 1 unread message",
);

A format string must not contain both implicit and explicit references:

strat("My name is {} {}. Do you like the name {0}?", ["Lemony", "Snicket"]);
// -> Error: cannot mix implicit & explicit formatting

Escape { and } characters by doubling it ( ie. {{ and }} produce { and } respectively ):

strat("{{}} creates an empty {} {}", ["object", "literal"]);
// -> "{} creates an empty object literal"

Dot notation may be used to reference object properties:

import { strat } from "jsr:@haltcase/strat";
import { assertEquals } from "jsr:@std/assert/equals";

const rick = { firstName: "Rick", lastName: "Sanchez" };
const morty = { firstName: "Morty", lastName: "Smith" };

assertEquals(
	strat("{0.firstName} {0.lastName} and {1.firstName} {1.lastName}", [
		rick,
		morty,
	]),
	"Rick Sanchez and Morty Smith",
);

0. may be omitted when referencing a property of {0}:

import { strat } from "jsr:@haltcase/strat";
import { assertEquals } from "jsr:@std/assert/equals";

const song = {
	title: "Handlebars",
	artist: "Flobots",
	album: "Fight With Tools",
};

assertEquals(
	strat("{title} | [{artist}] | {album}", song),
	"Handlebars | [Flobots] | Fight With Tools",
);

If the referenced property is a method, it is invoked with no arguments to determine the replacement:

import { strat } from "jsr:@haltcase/strat";
import { assertEquals } from "jsr:@std/assert/equals";

const album = {
	name: "The Death of Peace of Mind",
	artist: "Bad Omens",
	releaseDate: new Date("2022-02-25"),
};

assertEquals(
	strat("{name} was released {releaseDate.toISOString}.", album),
	"The Death of Peace of Mind was released 2022-02-25T00:00:00.000Z.",
);

assertEquals(
	strat("Listen to more from {artist.toUpperCase}", album),
	"BAD OMENS",
);

To pass arguments to a method, pass them as a comma delimited list, with a space after the method name:

import { strat } from "jsr:@haltcase/strat";
import { assertEquals } from "jsr:@std/assert/equals";

const person = {
	react(tired: string, mood: string) {
		if (tired) {
			if (mood === "sad") return "cried";
			return "rolled his eyes";
		} else {
			if (mood === "mad") return "broke stuff";
			return "shook his fist";
		}
	},
};

assertEquals(
	strat("Average Joe {react true, indifferent}.", person),
	"Average Joe rolled his eyes.",
);

Note that all arguments are passed as strings, so you'll have to parse them appropriately if you need, for example, a number or boolean.

However, you can use _ to pass the falsy null value in the argument list:

strat("Average Joe {react _, mad}.", person);
// -> "Average Joe broke stuff."

strat.create(transformers?: { ...functions })

You can create a new instance of strat by calling strat.create(). You may also optionally supply an object containing transformer functions that you can use in strat() to modify string replacements.

Transformers are very similar to a function you'd pass to Array#map(). They receive three arguments: the value on which it's being used, the key, and the full collection of replacements provided to the template.

transform(value: string, key: string, collection: [...values]): string

To use a transformer, call it by prefixing it with ! after the field name in the template string. For example, {reaction!exclaim} where exclaim was previously passed in the transformers object.

Here's a simple example operating only on the value argument:

import { create } from "jsr:@haltcase/strat";
import { assertEquals } from "jsr:@std/assert/equals";

const instance = create({
	exclaim: (value) => value.toUpperCase() + "!",
});

assertEquals(instance("Hello, {!exclaim}", "world"), "Hello, WORLD!");

And here's one that semi-intelligently pluralizes units:

import { create } from "jsr:@haltcase/strat";
import { assertEquals } from "jsr:@std/assert/equals";

type MiniUnitShape = {
	days: number;
	daysLabel: string;
};

type NonLabelKeys = Exclude<keyof MiniUnitShape, `${string}Label`>;

const instance = create({
	pluralize(_value, key, collection: MiniUnitShape[]) {
		const labelSuffix = "Label";

		const pluralUnit = key.slice(0, -labelSuffix.length) as NonLabelKeys;
		const singularUnit = pluralUnit.slice(0, -1);

		return collection[0][pluralUnit] === 1 ? singularUnit : pluralUnit;
	},
});

const template = instance("{days} {daysLabel!pluralize}");

assertEquals(template({ days: 2, daysLabel: "days" }), "2 days");
assertEquals(template({ days: 1, daysLabel: "days" }), "1 day");

see also

• logger-neue – refined logging utility that utilizes strat

development

strat is built with Deno and cross-published to npm for Node.js.

1. Clone the repo: git clone https://github.com/haltcase/strat.git
2. Move into the new directory: cd strat
3. Install dependencies: deno install
4. Run tests: deno test
5. Check code quality (lint, format, types): deno run qc
6. Build for npm: deno run build-npm

contributing

Pull requests and any issues found are always welcome.

1. Fork the project, and preferably create a branch named something like feat-make-better
2. Follow the development steps above but using your forked repo
3. Modify the source files as needed
4. Make sure all tests continue to pass, and it never hurts to have more tests
5. Push & pull request! 🎉

license

MIT © Bo Lingen / haltcase