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。