Parse a string function definition and return a function object. Does not use eval. Analisa uma definição de função em string e retorna um objeto de função. Não usa eval.

parseFunctionString.ts

class ParseFunctionString {
    /* Parse a string function definition and return a function object. Does not use eval.
     * @param {string} str
     * @return {function}
     *
     * Example:
     *  var f = function (x, y) { return x * y; };
     *  var g = parseFunction(f.toString());
     *  g(33, 3); //=> 99
     */
    parse(str): any {
        const isAsync = str.trim().startsWith('async');
        const fnBodyIdx = str.indexOf('{');
        const fnBody = str.substring(fnBodyIdx + 1, str.lastIndexOf('}'));
        const fnDeclare = str.substring(0, fnBodyIdx);
        const fnParams = fnDeclare.substring(fnDeclare.indexOf('(') + 1, fnDeclare.lastIndexOf(')'));
        const args = fnParams.split(',');

        if (isAsync) {
            const AsyncFunction = Object.getPrototypeOf(async () => {}).constructor;
            function AsyncFn(): any {
                return AsyncFunction.apply(this, args);
            }
            AsyncFn.prototype = AsyncFunction.prototype;
            // @ts-ignore
            return new AsyncFn();
        }
        function Fn(): any {
            return Function.apply(this, args);
        }
        Fn.prototype = Function.prototype;
        
        return new Fn().bind(this);
    }
}