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preload.worker.js
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preload.worker.js
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const COMMANDS = {
LOAD: 'LOAD',
LOAD_COMPLETE: 'LOAD_COMPLETE',
};
const preloadImageArray = (arr) => {
const promiseArr = [];
arr.forEach((imgUrl) => {
promiseArr.push(new Promise((resolve) => {
const request = new XMLHttpRequest();
request.responseType = 'blob';
request.onload = () => {
resolve({
path: imgUrl,
status: 'ok',
});
};
request.onerror = () => {
resolve({
path: imgUrl,
status: 'error',
});
};
request.open('GET', imgUrl, true);
request.send();
}));
});
return Promise.all(promiseArr);
};
this.addEventListener('message', (e) => {
const { data } = e;
switch (data.cmd) {
case COMMANDS.LOAD:
preloadImageArray(data.imageUrls).then(() => {
this.postMessage({ cmd: COMMANDS.LOAD_COMPLETE });
});
break;
default:
}
});