JavaScript中未捕获的类型错误

Question

I am creating the first phonegap application so that i followed one tutorial int that tut the following error should thrown in my logcat.

Uncaught TypeError: Cannot call method 'transaction' of undefined at file:///android_asset/www/js/index.js:40

" * " line is my 40th line

function saveDatas(details, cb) {
if(details.name == "") details.name = "[No Title]";
  *dbShell.transaction(function(tx) {*
    if(details.id == "")tx.executeSql("insert into nameDetail(name,age,city,occupation,date) values(?,?,?,?,?)",[details.name,details.age,details.city,details.occupation, new Date()]);
    else tx.executeSql("update nameDetail set name=?, age=?,city=?,occupation=?,date=? where id=?",[details.name,details.age,details.city,details.occupation, new Date(), details.id]);
}, dbErrHandler,cb);

}

Edit 1:

var dbShell;

function phoneReady() {
dbShell = window.openDatabase("Names", 1, "Names", 1000000);
dbShell.transaction(setUpTable, dbErrHandler, getDatas);

}

Full js file:

var dbShell;

function phoneReady() {
    dbShell = window.openDatabase("Names", 1, "Names", 1000000);
    dbShell.transaction(setUpTable, dbErrHandler, getDatas);

}

function dbErrHandler(err) {
    alert("Error : " + err.message + "\n Code" + err.code); }

function setUpTable(tx) {
    tx.executeSql("CREATE TABLE IF NOT EXISTS nameDetail(id INTEGER PRIMARY KEY,name,age,city,occupation,date)");

}

function getDatas() {
    dbShell.transaction(function(tx) {
        tx.executeSql("select name,age,city,occupation,date from nameDetail order by date desc", [], renderEntries, dbErrHandler);
    }, dbErrHandler); }

function renderEntries(tx, results) {
    if (results.rows.length == 0) {
        $("#mainContent").html("<p>Don't have any Details</p>");
    } else {
        var s = "";
        for (var i = 0; i < results.rows.length; i++) {
            s += "<li><a href='addEdit.html?id=" + results.rows.item(i).id + "'>" + results.rows.item(i).title + "</a></li>";
        }

        $("#noteTitleList").html(s);
        $("#noteTitleList").listview("refresh");
    } }

function saveDatas(details, cb) {    if(details.name == "") details.name = "[No Title]";
      dbShell.transaction(function(tx) {
        if(details.id == "")tx.executeSql("insert into nameDetail(name,age,city,occupation,date) values(?,?,?,?,?)",[details.name,details.age,details.city,details.occupation, new Date()]);
        else tx.executeSql("update nameDetail set name=?, age=?,city=?,occupation=?,date=? where id=?",[details.name,details.age,details.city,details.occupation, new Date(), details.id]);
    }, dbErrHandler,cb);
     }

function init() {
    document.addEventListener("deviceReady", phoneReady, false);
    $("#addEditForm").live("submit", function(e) {
        var data = {
            name:$("#mName").val(),
            age:$("#mAge").val(),
            city:$("#mCity").val(),
            occupation:$("#mOccupation").val(),
            id:$("#mId").val()
        };

        saveDatas(data, function() {
            $.mobile.changePage("index.html", {
                reverse: true
            });
        });
        e.preventDefault();
    });

    $("#homePage").live("homepage", function() {
        getDatas();
    });

    $("#editPage").live("pageshow", function() {
        var loc = window.location.hash;
        if (loc.indexOf("?") >= 0) {
            var qs = loc.substr(loc.indexOf("?") + 1, loc.length);
            var detailId = qs.split("=")[1];
            $("editFormSubmitButton").attr("disabled", "disabled");
            dbShell.transaction(function(tx) {
                tx.executeSql("select id,name,age,city,occupation from nameDetails where id=?", [detailId], function(tx, results) {
                    $("#mId").val(results.rows.item(0).id);
                    $("#mName").val(results.rows.item(0).name);
                    $("#mAge").val(results.rows.item(0).age);
                    $("#mCity").val(results.rows.item(0).city);
                    $("#mOccupation").val(results.rows.item(0).occupation);
                    $("#editFormSubmitButton").removeAttr("disabled");
                });
            }, dbErrHandler);
        } else {
            $("#editFormSubmitButton").removeAttr("disabled");
        }
    });

}

anybody suggest some solution ...

Answer 1

In JavaScript there is a difference in declaring and defining .

var dbShell;

Now dbShell is declared .

dbShell = "foo";

Now dbShell is defined .

If you do:

var dbShell;
dbShell.foo();

You will get: Uncaught TypeError: Cannot call method 'foo' of undefined