typescript-templater

A class for creating simple template dialects.

Usage

Browser or Deno

import Templater from "https://esm.sh/@jmcantrell/templater";

Node

npm install @jmcantrell/templater

import Templater from "@jmcantrell/templater";

Example

const dialect = new Templater("${", "}");
const greeting = dialect.compile("Hello, ${name}!");
console.log(greeting({ name: "you" })); // outputs: "Hello, you!"

Behavior

For this section, dialect is assumed to have the following definition:

const dialect = new Templater("${", "}");

The dialect above will render strings containing placeholders that look like ${name}:

const size = dialect.compile("${width}x${height}");
console.log(size(800, 600)); // outputs: "800x600"

Template strings with no placeholders will compile to a function that simply returns the string unchanged.

For example:

const greeting = dialect.compile("Hello!");

Is equivalent to:

const greeting = () => "Hello!";

As you might expect, multiple instances of the same placeholder will all be replaced:

const thrice = dialect.compile("${value} ${value} ${value}");
console.log(thrice({ value: "yeah!" })); // outputs: "yeah! yeah! yeah!"

When passing options to templates, any missing options will render those placeholders unchanged:

const greeting = dialect.compile("Hello, ${name}!");
console.log(greeting()); // outputs: "Hello, ${name}!"

Similarly, if any passed options don't have a corresponding placeholder, they will be ignored:

const greeting = dialect.compile("Hello, ${name}!");
console.log(greeting({ bogus: "foo" })); // outputs: "Hello, ${name}!"

You can give any placeholder a default value that will be used if no value is provided:

const greeting = dialect.compile("Hello, ${name=you}!");
console.log(greeting()); // outputs: "Hello, you!"

API

Creating a template dialect

const dialect = new Templater(prefix, suffix);

The constructor takes one argument that's expected to be an object with two properties, prefix and suffix.

The prefix parameter should be a string that will be the left side of a placeholder.

The suffix parameter should be a string that will be the right side of a placeholder.

For example, passing parameters like "{" and "}" will mean that placeholders in the template strings will be expected to look like {whatever}.

Compiling a template string

const compiled = dialect.compile(string);

Once a template dialect is created, the typical usage is compiling one or more template strings, and using those compiled templates to quickly render output many times over the life of your program. Compiling a template string means that all the hard work involved is only done once so that rendering is as quick as possible.

The returned compiled template is simply a function that accepts an object expected to contain placeholder values.

Rendering a template string without compilation

const rendered = dialect.render(string, options);

If you're testing a template string or know that it will only be used once, you can render a string directly, skipping the compile step.

For example, the following two pieces of code produce the same output string:

const greeting = dialect.compile("Hello, ${name}!");
console.log(greeting({ name: "you" }));

console.log(dialect.render("Hello, ${name}!", { name: "you" }));