interface RequestPending {
state: 'pending';
}
interface RequestError {
state: 'error';
error: string;
}
interface RequestSuccess {
state: 'ok';
pageText: string;
}
type RequestState = RequestPending | RequestError | RequestSuccess;
interface State {
currentPage: string;
requests: {[page: string]: RequestState};
}
function getUrlForPage(p: string) { return ''; }
function renderPage(state: State) {
const {currentPage} = state;
const requestState = state.requests[currentPage];
switch (requestState.state) {
case 'pending':
return `Loading ${currentPage}...`;
case 'error':
return `Error! Unable to load ${currentPage}: ${requestState.error}`;
case 'ok':
return `<h1>${currentPage}</h1>\n${requestState.pageText}`;
}
}
async function changePage(state: State, newPage: string) {
state.requests[newPage] = {state: 'pending'};
state.currentPage = newPage;
try {
const response = await fetch(getUrlForPage(newPage));
if (!response.ok) {
throw new Error(`Unable to load ${newPage}: ${response.statusText}`);
}
const pageText = await response.text();
state.requests[newPage] = {state: 'ok', pageText};
} catch (e) {
state.requests[newPage] = {state: 'error', error: '' + e};
}
}
위처럼 작성하면 모호함을 완전히 제거할 수 있습니다. 모든 요청은 정확히 하나의 상태로 맞아 떨어집니다.
<이펙티브 타입스크립트> (댄 밴더캅 지음, 장원호 옮김, 인사이트, 2021)