Custom Variable Providers

You can use a plain object like { "key": "value" }, or a new Map() instance to pass variables into format. You are not limited by that though!

If you'd like to pass other types of values into the template, you can create your own variable provider. The only requirement is that you have a get method which accepts a variable name, and returns the value corresponding to that variable as a string.

import fs from "fs";

class FileProvider {
  public get(key: string) {
    return fs.readFileSync(key).toString();
  }
}

// This project is built with node 22
format("This project is built with node {{ .nvmrc }}", new FileProvider());

You are limited to sync functions. If you need to perform potentially async operations to get values, consider using parseVariablesUsed to get the variable names first and gather values in advance.