runsly Html5教程 2021-12-14

HTML5 WebSQL四种基本操作的介绍

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Web SQL数据库API是一个独立的规范，在浏览器层面提供了本地对结构化数据的存储，已经被很多现代浏览器支持了。

我们通过一个简单的例子来了解下如何使用Web SQL API在浏览器端创建数据库表并存储数据。

<!doctype html>
<html>
<head>
    <script>
    var end;
    function setupDB() {
        return this.createDatabase().then(createTable).then(insertEntry).then(readEntry).then(printResult);
    }
    function createTable() {
        return new Promise(function(resovle, reject) {
            console.log("prepare to create table..." + Date.now());
            this._db.transaction(function(query) {
                query.executeSql('create table if not exists user(id unique, user, passwd)');
            });
            setTimeout(_createTableOK.bind(this, resovle), 1000);
        });
    }
    function _createTableOK(resovle) {
        console.log("table created successfully..." + Date.now());
        resovle();
    }
    function createDatabase() {
        return new Promise(function(resovle, reject) {
           console.log("prepare to create database..." + Date.now());
            this._db = openDatabase('mydb', '1.0', 'JerryTestdb', 1024);
            setTimeout(_createDatabaseOK.bind(this, resovle), 1000);
        });
    }
    function _createDatabaseOK(resovle) {
        console.log("database created successfully..." + Date.now());
        resovle(this._db);
    }
    function insertEntry() {
        return new Promise(function(resolve, reject) {
            this._db.transaction(function(query) {
                query.executeSql("insert into user values (1,'Jerry','1234')");
            });
            setTimeout(_insertEntryOK.bind(this, resolve), 1000);
        });
    }
    function _insertEntryOK(resolve) {
        console.log("entry inserted to table successfully..." + Date.now());
        resolve();
    }
    function readEntry() {
        return new Promise(function(resolve, reject) {
            this._db.transaction(function(query) {
                    query.executeSql('select * from user', [], function(u, results) {
                        setTimeout(_readEntryOK.bind(this, resolve, results), 1000);
                    }); // end of query.executeSql
                } // end of function(query)
           ); // end of this._db.transaction
        });
    }
    function _readEntryOK(resolve, oResult) {
        console.log("entry readed from DB successfully..." + Date.now());
        resolve(oResult);
    }
    function printResult(oResults) {
        for (var i = 0; i < oResults.rows.length; i++) {
            document.writeln('id: ' + oResults.rows[i].id);
            document.writeln('user: ' + oResults.rows[i].user);
            document.writeln('passwd: ' + oResults.rows[i].passwd);
        }
        end = true;
    }
    function work() {
        if (end) {
            clearInterval(handle);
        } else {
            console.log(" working..." + Date.now());
        }
    }
    setupDB();
    var handle = setInterval(work, 200);
    </script>
</head>
</html>

在浏览器里执行这个应用，会创建一个名叫mydb的数据库，里面一张名为“user”的数据库表，并且插入一条记录进去，然后从数据库表中读取中来，打印在浏览器上。