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<button id="btn">My Promise</button>
<div id="log"></div>

'use strict';

function myTestPromise() {
    document.getElementById("log").insertAdjacentHTML('beforeend', 'start' + '<br>');
    var func1 = new Promise(
        function(resolve, reject) {
           resolve([1, 2, 3]);
        }
    );
    func1.then(function(val) {
       document.getElementById("log").insertAdjacentHTML('beforeend', val + '<br>');
       val.push('A');
       return Promise.resolve(val);
    }).then(function(val) {
       document.getElementById("log").insertAdjacentHTML('beforeend', val + '<br>');
       val.push('B');
       return Promise.resolve(val);
    }).then(function(val) {
       document.getElementById("log").insertAdjacentHTML('beforeend', val + '<br>');
       val.push('C');
       return Promise.resolve(val);
	  }).then(function(val) {
       document.getElementById("log").insertAdjacentHTML('beforeend', val + '<br>');
    });
}

document.getElementById("btn").addEventListener("click", myTestPromise);