Get a Typescript typed environment variable value from `process.env` (NodeJS) with type casting for booleans, strings and numbers

env.ts

/**
 * Return an environment variable typed value from `process.env`.
 * It also supports a default value in case of `undefined`.
 *
 * The function will follow these steps to take a typed value:
 * 1. First it will try to get the env value from `process.env`.
 * 2. Then if `undefined` then it try with the default environment variable value if defined.
 * 3. Otherwise if the default value is `undefined` then it will return the Javascript default values:
 *     - Boolean: `false`
 *     - String: `""`
 *     - Number: `0`
 *
 * @param name string Environment variable name.
 * @param defaults an Optional default environment variable value when not found.
 * @returns env Typed value of the environment variable.
 */
function env (name: string, defaults?: string): string
function env (name: string, defaults?: boolean): boolean
function env (name: string, defaults?: number): number
function env (name: string, defaults?: string | boolean | number): string | boolean | number {
    const val: string = typeof process === "undefined" ? "" : (process.env && process.env[name] || "")

    switch (typeof defaults) {
        case "number": {
            if (!name || val.length === 0) return defaults || 0
            return Number.isNaN(val) ? (defaults || 0) : Number(val)
        }
        case "boolean":
            switch (val) {
                case "0":
                case "false":
                case "FALSE":
                    return false
                case "1":
                case "true":
                case "TRUE":
                    return true
                default: {
                    return defaults || false
                }
            }
        case "string":
        default:
            if (!name) return defaults || ""
            return val || defaults || ""
    }
}

Usage: See TypeScript Playground