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data.js
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data.js
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/**
* Copyright (c) Facebook, Inc. and its affiliates.
*
* This source code is licensed under the MIT license found in the
* LICENSE file in the root directory of this source tree.
*/
import {readCache} from './cache';
// TODO: clean up and move to react-data/fetch.
// TODO: some other data provider besides fetch.
// TODO: base agnostic helper like createResource. Maybe separate.
let sigil = {};
function readFetchMap() {
const cache = readCache();
if (!cache.has(sigil)) {
cache.set(sigil, new Map());
}
return cache.get(sigil);
}
export function fetch(url) {
const map = readFetchMap();
let entry = map.get(url);
if (entry === undefined) {
entry = {
status: 'pending',
result: new Promise(resolve => {
let xhr = new XMLHttpRequest();
xhr.onload = function() {
entry.result = JSON.parse(xhr.response);
entry.status = 'resolved';
resolve();
};
xhr.onerror = function(err) {
entry.result = err;
entry.status = 'rejected';
resolve();
};
xhr.open('GET', url);
xhr.send();
}),
};
map.set(url, entry);
}
switch (entry.status) {
case 'resolved':
return entry.result;
case 'pending':
case 'rejected':
throw entry.result;
default:
throw new Error();
}
}