easy way to understand javascript promises

promises.js

"use strict";

var p1 = new Promise( function(resolve) {
    resolve();
});

var p2 = new Promise( function(resolve) {
    resolve();
});

var p3 = new Promise( function(resolve) {
    resolve();
});

var p4 = Promise.resolve().then( function() {
    console.log(1);
    return p1.then( function() {
        console.log(2);
    });
}).then( function() {
    console.log(3);
    return p2.then( function() {
        console.log(4);
    });
}).then( function() {
    console.log(5);
    return p3;
}).then( function() {
    console.log(6);
    throw new Error();
}).then( function() {
    // Skipped
    console.log(7);
}).catch( function(error) {
    console.log(error);
}).then( function() {
    // Not skipped
    console.log(8);
    return 9;
});

Promise.resolve(p4).then( function(value) {
	console.log(value);  //-> 9
});