promisedemo.js

function triangle(x)
{
	if (x <= 1)
	{
		if (x == 1) return 1;
		else throw "Can't get triangle number of " + x;
	}
	return triangle(x - 1) + x;
}

function triangle_callback(x, cb)
{
	if (x <= 1)
	{
		if (x == 1) cb(1);
		else throw "Can't get triangle number of " + x;
	}
	else triangle_callback(x - 1, function(tri) {cb(tri + x);});
}

function triangle_promise(x)
{
	if (x <= 1)
	{
		return new Promise(function(resolve, reject) {
			if (x == 1) resolve(1);
			else throw "Can't get triangle number of " + x;
		});
	}
	return triangle_promise(x - 1).then(tri => tri + x);
}

function* triangle_gen(x)
{
	if (x <= 1)
	{
		if (x == 1) return 1;
		else throw "Can't get triangle number of " + x;
	}
	yield triangle_gen(x - 1).next().value + x;
}