asyncとawait
18687 ワード
asyncとawaitは実は戦術皮で、彼女の本質はPromiseで、毎回関数がPromiseの対象に帰るのでさえすれば、あなたはawaitそれを使うことができて、同期のプログラムの方式のように獲得することができます.
console.log("before");
const user = getUser(1);
console.log("Go: user", user);
console.log("after");
//callback
//promise
//asyn/await
function getUser(id) {
setTimeout(() => {
console.log("Get user from database");
return { id: id, username: "helloworld" };
}, 2000);
}
// ：
// before
// Go: user undefined
// after
// Get user from database
console.log("before");
const user = getUser(1, user => {
getRepositories(user, repos => {
repos.map(repo => {
console.log(repo);
});
});
});
console.log("after");
//callback
//promise
//asyn/await
function getUser(id, callback) {
setTimeout(() => {
console.log("Get user from database");
callback({ id: id, username: "helloworld" });
}, 2000);
}
function getRepositories(username, callback) {
setTimeout(() => {
console.log("get Repositories from database");
callback([1, 2, 3]);
}, 1000);
}
//
// before
// after
// Get user from database
// get Repositories from database
// 1
// 2
// 3
console.log("before");
getUser(1).then(res => {
console.log(res);
//promise
//asyn/await
function getUser(id) {
return new Promise((resolve, reject) => {
setTimeout(() => {
console.log("Get user from database");
resolve({ id: id, username: "helloworld" });
}, 2000);
});
}
function getRepositories(username, callback) {
setTimeout(() => {
console.log("get Repositories from database");
callback([1, 2, 3]);
}, 1000);
}
console.log("before");
getInfo();
console.log("after");
//asyn/await
async function getInfo() {
const user = await getUser(1);
console.log("Go: getInfo -> user", user);
const abc = await getRepositories(1);
console.log("Go: getInfo -> abc", abc);
}
function getUser(id) {
return new Promise((resolve, reject) => {
setTimeout(() => {
resolve({ id: id, username: "helloworld" });
}, 2000);
});
}
function getRepositories(username) {
return new Promise((resolve, rerject) => {
setTimeout(() => {
console.log("get Repositories from database");
resolve([1, 2, 3]);
}, 1000);
});
}