第十天
<p>一些新特性</p>
<pre><code class="language-javascript"> const cars = {
'🚙BMW': '10',
'🚘Tesla': '5',
'🚖Lamborghini': '0'
}
Object.entries(cars).map(([name, count]) => {
//padEnd appends ' -' until the name becomes 20 characters
//padStart prepends '0' until the count becomes 3 characters.
console.log(`${name.padEnd(20, ' -')} Count: ${count.padStart(3, '0')}`)
});
以下是打印的结果：
"🚙BMW - - - - - - - Count: 010"
"🚘Tesla - - - - - - Count: 005"
"🚖Lamborghini - - - Count: 000"</code></pre>
<pre><code class="language-javascript">async function doubleAndAdd(a, b) {
a = await doubleAfter1Sec(a);
b = await doubleAfter1Sec(b);
return a + b;
}
doubleAndAdd('one', 2)
.then(console.log)
.catch(console.log); //NaN
function doubleAfter1Sec(param) {
return new Promise((resolve, reject) => {
setTimeout(function() {
let val = param * 2;
isNaN(val) ? reject(NaN) : resolve(val);
}, 1000);
});
}</code></pre>