I have the following code in one of my function. I have an array 'arr' which is working correctly when used inside if{}. But its now working when using outside it. Can anyone point me what I am missing.
function runQueries()
{
var arr = new Array;
db.transaction (function (transaction)
{
var sql = "SELECT * FROM incomecategory";
transaction.executeSql (sql, undefined,
function (transaction, result)
{
if (result.rows.length)
{
for (var i = 0; i < result.rows.length; i++)
{
var row = result.rows.item (i);
var categoryname = row.categoryname;
arr[i] = categoryname;
}
//alert(arr[0]); // It works
}
else
{
}
}, error);
});
//alert (arr[0]); // It doesn't work.
}
It's asynchronous behavior. Your alert at the bottom of the code is probably executed before the database query.
Related
I've been working on a project and I'm currently working on a function which dynamically creates a dictionary data structure. The key used is the roll number of the student, and the value is the student's name.
But I'm unable to iterate through this dictionary. I've tried displaying the dictionary on console, but all I could see is an empty dictionary. I could see the elements in it, only if I expand it further. And when I display length using Obj.length on console, it displays 'undefined'. I've read on other questions that Obj.length only works on arrays(i.e., enumerable types), and I've tried using an array instead of a dictionary. In that case, it shows an empty array and would not show values unless I manually expand it. I've also tried Obj.keys() method on the dictionary, and I've encountered the same issue.
This is the function's code:
function dictGenerator(rollnos, selectedValue) {
var dict = {};
for(let i = 0; i < rollnos.length; i++) {
get(child(dbref, "RegisterNos/" + rollnos[i])).then((snapshot)=>{
if(Object.keys(snapshot.val()).length-1 == selectedValue){
dict[rollnos[i]] = snapshot.val()["name"];
}
});
}
console.log(dict);
console.log(dict.length);
}
}
Any help on how I could iterate through my dictionary would be appreciated, Thank you.
Edit:
code implementation using promises.
function dictGenerator(regnos, selectedValue) {
const get_dict = async () => {
var dict = {};
for(let i = 0; i < regnos.length; i++){
get(child(dbref, "RegisterNos/" + regnos[i])).then((snapshot)=>{
if(Object.keys(snapshot.val()).length-1 == selectedValue){
dict[regnos[i]] = snapshot.val()["name"];
}
});
}
return dict;
};
get_dict().then((dict) => {
console.log(dict);
});
}
Basing on comments made by VALZ and JaredSmith, this is the working code:
function dictGenerator(regnos, selectedValue) {
const get_dict = async () => {
var dict = {};
for(let i = 0; i < regnos.length; i++){
await get(child(dbref, "RegisterNos/" + regnos[i])).then((snapshot)=>{
if(Object.keys(snapshot.val()).length-1 == selectedValue){
dict[regnos[i]] = snapshot.val()["name"];
}
});
}
return dict;
};
get_dict().then((dict) => {
console.log(dict);
});
}
}
I really try my damndest not to ask, but i have to at this point before I tear my hair out.
By the time the js interpreter gets to this particular method, I can print it to the console no problem, it is an array of "event" objects. From FireBug I can see it, but when I try to set a loop to do anything with this array its as if it doesn't exist. I am absolutely baffled......
A few things:
I am a newbie, I have tried a for(var index in list) loop, to no avail, I have also tried a regular old for(var i = 0; i < listIn.length; i++), and I also tried to get the size of the local variable by setting var size = listIn.length.
As soon as I try to loop through it I get nothing, but I can access all the objects inside it from the FireBug console no problem. Please help, even just giving me a little hint on where I should be looking would be great.
As for the array itself, I have no problems with getting an array back from PHP in the form of: [{"Event_Id":"9", "Title":"none"}, etc etc ]
Here is my code from my main launcher JavaScript file. I will also post a sample of the JSON data that is returned. I fear that I may be overextending myself by creating a massive object in the first place called content, which is meant to hold properties such as DOM strings, settings, and common methods, but so far everything else is working.
The init() function is called when the body onload is called on the corresponding html page, and during the call to setAllEvents and setEventNavigation I am lost.
And just to add, I am trying to learn JavaScript fundamentals before I ever touch jQuery.
Thanks
var dom, S, M, currentArray, buttonArray, typesArray, topicsArray;
content = {
domElements: {},
settings: {
allContent: {},
urlList: {
allURL: "../PHP/getEventsListView.php",
typesURL: "../PHP/getTypes.php",
topicsURL: "../PHP/getTopics.php"
},
eventObjArray: [],
buttonObjArray: [],
eventTypesArray: [],
eventTopicsArray: []
},
methods: {
allCallBack: function (j) {
S.allContent = JSON.parse(j);
var list = S.allContent;
for (var index in list) {
var event = new Event(list[index]);
S.eventObjArray.push(event);
}
},
topicsCallBack: function(j) {
S.eventTopicsArray = j;
var list = JSON.parse(S.eventTopicsArray);
topicsArray = list;
M.populateTopicsDropDown(list);
},
typesCallBack: function(j) {
S.eventTypesArray = j;
var list = JSON.parse(S.eventTypesArray);
typesArray = list;
M.populateTypesDropDown(list);
},
ajax: function (url, callback) {
getAjax(url, callback);
},
testList: function (listIn) {
// test method
},
setAllEvents: function (listIn) {
// HERE IS THE PROBLEM WITH THIS ARRAY
console.log("shall we?");
for(var index in listIn) {
console.log(listIn[index]);
}
},
getAllEvents: function () {
return currentArray;
},
setAllButtons: function (listIn) {
buttonArray = listIn;
},
getAllButtons: function () {
return buttonArray;
},
setEventNavigation: function(current) {
// SAME ISSUE AS ABOVE
var l = current.length;
//console.log("length " + l);
var counter = 0;
var endIndex = l - 1;
if (current.length < 4) {
switch (l) {
case 2:
var first = current[0];
var second = current[1];
first.setNextEvent(second);
second.setPreviousEvent(first);
break;
case 3:
var first = current[0];
var second = current[1];
var third = current[2];
first.setNextEvent(second);
second.setPreviousEvent(first);
second.setNextEvent(third);
third.setPreviousEvent(second);
break;
default:
break;
}
} else {
// do something
}
},
populateTopicsDropDown: function(listTopics) {
//console.log("inside topics drop");
//console.log(listTopics);
var topicsDropDown = document.getElementById("eventTopicListBox");
for(var index in listTopics) {
var op = document.createElement("option");
op.setAttribute("id", "dd" + index);
op.innerHTML = listTopics[index].Main_Topic;
topicsDropDown.appendChild(op);
}
},
populateTypesDropDown: function(listTypes) {
//console.log("inside types drodown");
//console.log(listTypes);
var typesDropDown = document.getElementById("eventTypeListBox");
for(var index2 in listTypes) {
var op2 = document.createElement("option");
op2.setAttribute("id", "dd2" + index2);
op2.innerHTML = listTypes[index2].Main_Type;
typesDropDown.appendChild(op2);
}
}
},
init: function() {
dom = this.domElements;
S = this.settings;
M = this.methods;
currentArray = S.eventObjArray;
buttonArray = S.buttonObjArray;
topicsArray = S.eventTopicsArray;
typesArray = S.eventTypesArray;
M.ajax(S.urlList.allURL, M.allCallBack);
//var tempList = currentArray;
//console.log("temp array length: " + tempList.length);
M.setAllEvents(currentArray);
M.testList(currentArray);
M.setEventNavigation(currentArray);
//M.setEventNavigation();
M.ajax(S.urlList.topicsURL, M.topicsCallBack);
M.ajax(S.urlList.typesURL, M.typesCallBack);
}
};
The problem you have is that currentArray gets its value asynchronously, which means you are calling setAllEvents too soon. At that moment the allCallBack function has not yet been executed. That happens only after the current running code has completed (until call stack becomes emtpy), and the ajax request triggers the callback.
So you should call setAllEvents and any other code that depends on currentArray only when the Ajax call has completed.
NB: The reason that it works in the console is that by the time you request the value from the console, the ajax call has already returned the response.
Without having looked at the rest of your code, and any other problems that it might have, this solves the issue you have:
init: function() {
dom = this.domElements;
S = this.settings;
M = this.methods;
currentArray = S.eventObjArray;
buttonArray = S.buttonObjArray;
topicsArray = S.eventTopicsArray;
typesArray = S.eventTypesArray;
M.ajax(S.urlList.allURL, function (j) {
// Note that all the rest of the code is moved in this call back
// function, so that it only executes when the Ajax response is
// available:
M.allCallBack(j);
//var tempList = currentArray;
//console.log("temp array length: " + tempList.length);
M.setAllEvents(currentArray);
M.testList(currentArray);
M.setEventNavigation(currentArray);
//M.setEventNavigation();
// Note that you will need to take care with the following asynchronous
// calls as well: their effect is only available when the Ajax
// callback is triggered:
M.ajax(S.urlList.topicsURL, M.topicsCallBack); //
M.ajax(S.urlList.typesURL, M.typesCallBack);
});
}
How would I access the values of 'timestamp' and 'usage' in the following example,
function executeReadingsQuery(query, postQueryProcessing) {
var d = new $.Deferred();
var processing = function(tx, results) {
var result = [];
var len = results.rows.length;
for ( var i = 0; i < len; i++) {
result.push({
"timestamp" : moment(results.rows.item(i).timeStamp),
"usage" : results.rows.item(i).usage
});
}
if (postQueryProcessing) {
result = postQueryProcessing(result);
}
d.resolve(result);
};
executeQuery(query, processing);
return d;
}
A function that builds a query string will subsequently call the above function,
function getReadingsInternal(noOfReadings, postQueryProcessing) {
var query = "SELECT * from usage ORDER BY timestamp DESC limit " + noOfReadings.toString();
return executeReadingsQuery(query, postQueryProcessing);
}
And then there is another function that exposes the entire functionality globally,
getReadings : function(noOfReadings) {
return getReadingsInternal(noOfReadings);
}
The original function (the first one listed) is within a Variable called WNDatabase
So I can access the function with a call that looks like this
WNDatabase.getReadings(30)
But I would like to be able to also globally access the values of timestamp and usage which populate the result[] array of the deferred object.
It seems that it is not possible to do something like this
$.when(WNDatabase.getReadings(30)).done(function() {
for(var i=0; i<7; i++){
console.log(this[i].usage);
}
});
So what would one do in this event?
This is driving me crazy. I'm just trying to print out an array and it's not working. What am I missing? The results variable is returning "undefined" which much mean my for loop isn't working correctly. Everything else works properly, the console.log I have correctly displays the fields are added to the array.
// The list of accounts array.
var accountsArray = [];
function addAccount() {
// Take fields and put user data into varables.
var accountName = document.getElementById('accountName').value;
var accountBalance = document.getElementById('accountBalance').value;
var accountType = document.getElementById("accountType");
var accountTypeSelected = accountType.options[accountType.selectedIndex].text;
var accountCurrency = document.getElementById("accountCurrency");
var accountCurrencySelected = accountCurrency.options[accountCurrency.selectedIndex].text;
// Put these variables into the array.
accountsArray.push(accountName);
accountsArray.push(accountBalance);
accountsArray.push(accountTypeSelected);
accountsArray.push(accountCurrencySelected);
// Items added to the array, logged.
console.log('user added: ' + accountsArray);
}
function accountsListHtml() {
var results;
// Loop through the array
for (var i = 0; i < accountsArray.length; i++) {
results = accountsArray[i];
}
document.getElementById('accountsList').innerHTML = results;
}
Here's a link to all the files. It's an iOS web app using Framework7. Balance Pro
You are calling accountsListHtml() in body.onload. At that point accountsArray is empty.
I can't find any other possibility to call accountsListHtml() on that page you linked to.
Add one line inside function addAccount() and it will work:
function addAccount() {
/* vour code */
console.log('user added: ' + accountsArray);
accountsListHtml(); // add this line
}
Try changing results = accountsArray[i]; to results += accountsArray[i];.
Update
And initialize results with an empty string, for example :)
for (var i = 0; i < accountsArray.length; i++) {
results = accountsArray[i];
}
The statement in the for loop i.e. results = accountsArray[i]; overwrites the variable results evry loop run. You could change the statement to :
results += accountsArray[i].toString();
and initialise results to an empty string.
The following works for me: http://jsfiddle.net/95ztrmk3/13/
HTML:
<div id="accountsList"></div>
JS:
// The list of accounts array.
var accountsArray = [];
addAccount();
accountsListHtml();
function addAccount() {
// Take fields and put user data into varables.
var accountName = "John Doe";
var accountBalance = "500.00";
var accountTypeSelected = "Checking"
var accountCurrencySelected = "USD";
// Put these variables into the array.
accountsArray.push(accountName);
accountsArray.push(accountBalance);
accountsArray.push(accountTypeSelected);
accountsArray.push(accountCurrencySelected);
// Items added to the array, logged.
console.log('user added: ' + accountsArray);
}
function accountsListHtml() {
var results = [];
// Loop through the array
for (var i = 0; i < accountsArray.length; i++) {
results += accountsArray[i] + " ";
}
document.getElementById('accountsList').innerHTML = results;
console.log(results);
}
Assuming the input isn't malformed or otherwise weird. I made sure Javascript recognizes results is an empty array and not a string or something: var results = []
Thanks for the help in advance.
I'm working on an practice assigment using Phonegap and Javascript. Long story short: I need to use Parse.com to store information about some Lego minifigures. The problem I'm having right now is due mostly to my inexperience in Javascript.
I'm working on letting the user add tags to the figures. The user enters them, separated by comma, and I then split the string. That's working OK.
Now, I need to add the tags that don't exist yet to my database. For this, I search for any tags with that description (using query.find) and then, if it exists, I don't create it, I just modify the relationship. If it doesn't exist, I create it and then modify the relationship.
My problem is: I can't seem to be able to access the tag description (the string) from within the success callback of query.find. I'm pretty sure it's because of the scope. Is there any proper way to access variables from withing a success callback, besides the results array?
My current code is as follows:
var Figure = Parse.Object.extend("Figure");
var Tag = Parse.Object.extend("Tag");
var nombre = $('#nombre').val();
var serie = $('#serie').val();
var figure = new Figure({"Name":nombre,"Series":serie});
var tags = $('#tags').val();
res = tags.split(","); //split the
figure.save().then(function() {
for (var i = 0; i < res.length; i++) { //for each tag
var query = new Parse.Query(Tag); //create the query.
query.equalTo("Description", res[i]);
query.find( {//execute query
success: function(results, res[i]) {
if (results.length > 0){ //if there are results.
var tag = results[0]; //get the tag
var relation_tag = tag.relation("figures"); //get the relation
relation_tag.add(figure); //add figure to relation
tag.save();
}
else { //if there are no results, the tag does not exist.
new_tag = new Tag({"Description":res[i]});
//ABOVE THIS LINE: res[i] is always undefined.
var relation_tag = new_tag.relation("figures"); //get the relation
relation_tag.add(figure); //add the figure
new_tag.save();
}
},
//error with query
error: function() {
alert("ERROR");
}
});
}
}, function(error) {
alert("No se pudo guardar la figura");
});
In the success callback, res[i] always is undefined, I assume that it's because of the scope.
This is a very common problem in async Javascript programming. You are doing something like this:
for (var i = 0; i < array.length; i++) {
anAsyncFunction(function(result) { // inner function
doSomethingWith(array[i]);
}
}
The problem is that in Javascript functions store outer variables by reference and not by value, which means that a function looks up the value of a variable from an outer scope, when it is executed and not when it is defined. Since the code is async the the inner function is called after the for loop completed and at this point we have i === array.length, so array[i] === array[array.length] === undefined.
To avoid this you can use an immediately invoked function expression (IIFE, pronounced "iffy"):
for (var i = 0; i < array.length; i++) {
anAsyncFunction((function(j) { // IIFE
return function innerFunction(result) { // inner function
doSomethingWith(array[j]); // j instead of i
}
})(i); // passing "value of i"
}
Because the IIFE is invoked immediately, the current value is of i is passed and stored into j and when the inner function executes it uses the correct value.
So in your case this should work:
success: (function(j) { // IIFE
return function(results) {
if (results.length > 0) {
var tag = results[0];
var relation_tag = tag.relation("figures");
relation_tag.add(figure);
tag.save();
}
else { //if there are no results, the tag does not exist.
new_tag = new Tag({"Description":res[j]}); // j instead of i
var relation_tag = new_tag.relation("figures");
relation_tag.add(figure);
new_tag.save();
}
}
})(i) // pass "value of i"
If you prefer, you can also pass the description itself instead of just the index to the IIFE (I think I would do it that way):
success: (function(description) { // IIFE
return function(results) {
if (results.length > 0) {
var tag = results[0];
var relation_tag = tag.relation("figures");
relation_tag.add(figure);
tag.save();
}
else { //if there are no results, the tag does not exist.
new_tag = new Tag({"Description":description}); // description
var relation_tag = new_tag.relation("figures");
relation_tag.add(figure);
new_tag.save();
}
}
})(res[i]) // pass description
var Tag = Parse.Object.extend("Tag");
var query = new Parse.Query(Tag);