advantage:
- In the asynchronous execution process, clearly separate the execution code from the code that processes the result
Example 1. Generate a random number between 0 and 2. If it is less than 1, it will return success after waiting for a period of time, otherwise it will return failure:
'use strict';
// 清除log:
var logging = document.getElementById('test-promise-log');
while (logging.children.length > 1) {
logging.removeChild(logging.children[logging.children.length - 1]);
}
// 输出log到页面:
function log(s) {
var p = document.createElement('p');
p.innerHTML = s;
logging.appendChild(p);
}
new Promise(function (resolve, reject) {
log('start new Promise...');
var timeOut = Math.random() * 2;
log('set timeout to: ' + timeOut + ' seconds.');
setTimeout(function () {
if (timeOut < 1) {
log('call resolve()...');
resolve('200 OK');
}
else {
log('call reject()...');
reject('timeout in ' + timeOut + ' seconds.');
}
}, timeOut * 1000);
}).then(function (r) {
log('Done: ' + r);
}).catch(function (reason) {
log('Failed: ' + reason);
});