ES6 Promise Example

An example of es6 promises. How to define a promise and catch potential errors. Uses a timer function to simulate an ajax request to the server.

by stratdaz

Babel + JSX

// ES6 Promise Example

// server
// -----------------------------------------------------
// Imagine this array lives in your server
const people = [
	{name: 'John Doe', age: '30'},
	{name: 'Jane Doe', age: '24'}
];

// client
// -----------------------------------------------------

// function that simulates an AJAX call to our
// imaginary server, where the people array lives.
// The call may succeed or fail.
const simulateAJAXCall = (index, cb) => {
	let chance = Math.random();
	let isSuccess= (chance <= 0.80) ? true : false;
	
	return setTimeout(() => {
		if (isSuccess) {
			return cb(people[index]);
		}
		else {
			return cb(null);
		}
	}, 1000)
}

// Function that returns a promise to search
// a person according to his index
const getPerson = (index) => {
	
	// The promise resolves if the data comes back
	// successfully and it rejects in case of an error
	return new Promise((resolve, reject) => {
		
		console.log('fetching person...');
		simulateAJAXCall(index, (data) => {
		
			if (data === null) {
				reject('Something went wrong!');
			}
			
			resolve(data);
		});
	});
}

// Call getPerson, which will return a promise.
// If the promise resolves, then log the person,
// if there's an error, it will go to the catch
// block and be handled there.
getPerson(0).then(person => {

	console.log(person);
}).catch(error => {

	console.log(error);
});