Last week I was working on build tasks to daemonise some of the services we intend to use for our project. I decided to use forever and ended up with a call that looks something like this:

let task = execForeverCommand('start', 'path/to/service');

or

let task = execForeverCommand('start', 'path/to/service', 'some', 'other', 'option');

The execForeverCommand would build up a command to execute by concatenating a variable length list of function arguments into one single string. What follows are three different approaches I took to build up that string based off of those arguments. By the way a function that accepts a variable number of arguments is also known as a variadic function.

My initial intention was to just use arguments.join(" "); however function arguments are not an array, instead they are an Array like object, therefore I opted to use a for-in loop:

function execForeverCommand() {
    let commands = '';
    for (var argument in arguments) {
        if(arguments.hasOwnProperty(argument)) {
            commands += ' ' + arguments[argument];
        }
    }

    return shell.task('./node_modules/forever/bin/forever ' + commands);
}

That worked, but is very verbose. Having a working solution, I spent some time reading through the MDN article I referenced above in more detail. I straight away realised that I could change the code to use Array.prototype.slice.call and combine that with my initial plan:

function execForeverCommand() {
    let commands = Array.prototype.slice.call(arguments).join(" ");

    return shell.task('./node_modules/forever/bin/forever ' + commands);
}

Now those astute readers might have spotted the use of let in these functions. On this project we are using ES6 features (with the assistance of Babel). This gave me a third option: Rest Parameters. Thanks to rest parameters I rewrote the function one last time, effetively going full circle and implementing my originally intended solution, i.e. by using Array.prototype.join().:

function execForeverCommand(...commands) {
    return shell.task('./node_modules/forever/bin/forever ' + commands.join(" "));
}