function-arguments.js

function functionArguments(fn) {
    if (fn.length > 0) {
        var fnString = Function.prototype.toString.call(fn);
        var firstIndex = fnString.indexOf('(');
        var lastIndex = fnString.indexOf(')');
        
        if (firstIndex > -1 && lastIndex > firstIndex) {
            firstIndex++;
            
            return fnString.substr(firstIndex, lastIndex - firstIndex).replace(/\s+/g, '').split(',');
        }
    }
    
    return [];
}

function-arguments.ts

function functionArguments(fn:Function):Array<string> {
    if (fn.length > 0) {
        let fnString = Function.prototype.toString.call(fn);
        let firstIndex = fnString.indexOf('(');
        let lastIndex = fnString.indexOf(')');
        
        if (firstIndex > -1 && lastIndex > firstIndex) {
            firstIndex++;
            
            return fnString.substr(firstIndex, lastIndex - firstIndex).replace(/\s+/g, '').split(',');
        }
    }
    
    return [];
}