Make a static template literal string come alive

templit.js

function templit(tpl, tag) {
    let exec;
    return (data) => {
        if (!exec) {
            const vars = Object.getOwnPropertyNames(data).map((key) => `${key} = this['${key}']`);
            exec = tag == null
                ? new Function(`var ${vars.join(',')}; return \`${tpl}\``)
                : new Function('__tag', `var ${vars.join(',')}; return __tag\`${tpl}\``);
        }
        return tag == null ? exec.call(data) : exec.call(data, tag);
    };
}

// Usage:

// Create a template and execute it
const addition = templit('${a} + ${b} = ${a + b}');
addition({a: 1, b: 2}); //=> "1 + 2 = 3"

// Use a tagged template function as an optional second argument
const status = templit('status: ${status}', (strings, ...values) => {
    return strings.raw.reduce((acc, str) => acc + values.shift().toUpperCase() + str);
});
status({status: 'ONLINE'}); //=> "message: HELLO WORLD"