javascript - how to make a function that returns sql result set with jQuery? -

i want make function return value of sql result set list (datalite).the problem is, can't read value of variable(datalite) outside db.transaction, return null value . new javascript , jquery hope can find answer here. here's part of function

function functiona(){     var datalite=null;     db.transaction(function (tx) {        tx.executesql('select * tablea', [], function (tx, results) {        var len = results.rows.length, i;        msg = "<p>found rows: " + len + "</p>";        alert(msg);        datalite=results.rows;         }, null);     });     alert(datalite+'>>>');     return datalite; } 

you can't return asynchronous code, data not yet available when function returns, come later. such situations (ajax requests, animations, etc.) have patterns. 1 callbacks:

function functiona(callback) {     db.transaction(function (tx) {         tx.executesql('select * tablea', [], function (tx, results) {             callback(results.rows);         }, null);     }); }  functiona(function(data) {     console.log(data); }); 

the second 1 promise pattern:

function functiona(callback) {     return new promise(function(resolve) {         db.transaction(function (tx) {             tx.executesql('select * tablea', [], function (tx, results) {                 resolve(results.rows);             }, null);         });     }); }  functiona().then(function(data) {     console.log(data); }); 

the second 1 more powerful , advanced, , gives several additional benefits simple callback don't offer. in basic case both work fine.

also make sure read this post on similar topic.