2020-03-22 03:23:11 +05:30
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<!DOCTYPE html>
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<html>
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<head>
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<meta charset="utf-8">
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</head>
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<body>
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2020-03-22 03:50:13 +05:30
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<button id="doit">Do It 3!</button>
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<script type="text/javascript">
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2020-03-22 03:23:11 +05:30
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function reqAsPromise(req) {
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return new Promise((resolve, reject) => {
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req.addEventListener("success", event => resolve(event.target.result));
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req.addEventListener("error", event => reject(event.target.error));
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});
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}
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function txnAsPromise(txn) {
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return new Promise((resolve, reject) => {
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txn.addEventListener("complete", resolve);
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txn.addEventListener("abort", reject);
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});
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}
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async function main() {
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2020-03-22 03:50:13 +05:30
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try {
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2020-03-22 03:23:11 +05:30
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2020-03-22 03:50:13 +05:30
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const openReq = window.indexedDB.open("two-read-write-txn", 1);
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openReq.onupgradeneeded = (ev) => {
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const db = ev.target.result;
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const store = db.createObjectStore("test", {keyPath: "id"});
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store.add({id: 6});
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};
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const db = await reqAsPromise(openReq);
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console.log("open txn1");
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const txn1 = db.transaction("test", "readwrite");
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const test1 = txn1.objectStore("test");
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console.log("request value1");
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const value1 = await reqAsPromise(test1.get(6));
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console.log("value1", value1);
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value1.previous = 5;
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value1.next = null;
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2020-03-22 03:23:11 +05:30
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2020-03-22 03:50:13 +05:30
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let txn2, test2, prom2, value2;
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2020-03-22 03:23:11 +05:30
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2020-03-22 03:50:13 +05:30
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// prevent deadlock
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(async function() {
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console.log("open txn2");
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txn2 = db.transaction("test", "readwrite");
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test2 = txn2.objectStore("test");
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console.log("request value2");
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prom2 = reqAsPromise(test2.get(6));
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value2 = await prom2;
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console.log("read value2");
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})();
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console.log("write value1");
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test1.put(value1);
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await txnAsPromise(txn1);
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2020-03-22 03:23:11 +05:30
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2020-03-22 03:50:13 +05:30
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await prom2;
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console.log("value2", value2);
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value2.next = 7;
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console.log("write value2");
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test2.put(value2);
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await txnAsPromise(txn2);
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2020-03-22 03:23:11 +05:30
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2020-03-22 03:50:13 +05:30
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const txn3 = db.transaction("test", "readonly");
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const value3 = await reqAsPromise(txn3.objectStore("test").get(6));
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2020-03-22 03:23:11 +05:30
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2020-03-22 03:50:13 +05:30
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alert("done " + JSON.stringify(value3));
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} catch (err) {
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alert(`error ${err.message} ${err.name} ${err.stack}`);
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}
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2020-03-22 03:23:11 +05:30
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}
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document.getElementById("doit").addEventListener("click", main);
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</script>
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</body>
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</html>
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