So a list of things walk into a bar . . .

question.js

// TODO: turn this into a "three guys walk into a bar" joke....


/*
You have a list of things you need process, items. In our case, times in seconds.

Use "processItemAsynchronously(timeInMilliseconds)" on each item in "items", while processing the items one at a time.

Each item completes in random time, asynchronously.

The question is how to do a list of asynchronous things, one at a time, waiting for the current item to finish before starting the next.
*/

const items = [100, 300, 400, 500, 600, 100, 300, 600, 200, 300, 400];

const processItemAsynchronously = (timeInMilliseconds) => {
    return new Promise((resolve) => {
        console.log('starting %s', timeInMilliseconds)
        setTimeout(() => {
            resolve('Done after ' + timeInMilliseconds + 'ms');
        }, timeInMilliseconds);
    });
};

const processList = (action, items) => {
	if (items.length > 0) {
    	action(items[0])
        	.then((message) => {
            	console.log(message);
                processList(action, items.slice(1, items.length));
            })
    }
}

// Do not wait for current item to complete before starting the next one
//items.forEach((item) => processItemAsynchronously(item).then((message) => console.log(message)))

// Wait for current item to complete before starting the next one
//processList(processItemAsynchronously, items);