promise 与 await 的互换

Rewriting promise code with async/await
Let's look back at a simple fetch example that we saw in the previous article:

fetch('coffee.jpg')
.then(response => {
if (!response.ok) {
throw new Error(HTTP error! status: ${response.status});
}
return response.blob();
})
.then(myBlob => {
let objectURL = URL.createObjectURL(myBlob);
let image = document.createElement('img');
image.src = objectURL;
document.body.appendChild(image);
})
.catch(e => {
console.log('There has been a problem with your fetch operation: ' + e.message);
});
By now, you should have a reasonable understanding of promises and how they work, but let's convert this to use async/await to see how much simpler it makes things:

async function myFetch() {
let response = await fetch('coffee.jpg');

if (!response.ok) {
throw new Error(HTTP error! status: ${response.status});
}

let myBlob = await response.blob();

let objectURL = URL.createObjectURL(myBlob);
let image = document.createElement('img');
image.src = objectURL;
document.body.appendChild(image);
}
}

myFetch()
.catch(e => {
console.log('There has been a problem with your fetch operation: ' + e.message);
});
It makes code much simpler and easier to understand — no more .then() blocks everywhere!