Develop Reference

How to convert Javascript array to JSON string

I have an array called values which has this data
var values=new Array();
values.push("english":"http://www.test.in/audio_ivrs/sr_listenglishMSTR001.wav");
values.push("kannada":"http://www.test.in/audio_ivrs/sr_listfrenchMSTR001.wav");
When I do JSON.stringify(values) I get values with square brackets, but I need a JSON string a shown below with urllist appended at the first.
{
"urlList":{
"english":"http://www.test.in/audio_ivrs/sr_listenglishMSTR001.wav",
"kannada":"http://www.test.in/audio_ivrs/sr_listfrenchMSTR001.wav"
}
}

Your code as you've defined it will give you errors. This is not valid JavaScript; you can't create an array element like this.
values.push("english":"http://www.test.in/audio_ivrs/sr_listenglishMSTR001.wav");
If you want the structure you've specified in your question then you'll need to use a nested object rather than an array to contain the key/value pairs.
var values = {
urlList: {}
};
values.urllist.english = "http://www.test.in/audio_ivrs/sr_listenglishMSTR001.wav";
values.urllist.kannada = "http://www.test.in/audio_ivrs/sr_listfrenchMSTR001.wav";
DEMO
HOWEVER...
Let's assume for a moment that what you meant to code was this (note the curly braces):
var values=new Array();
values.push({"english":"http://www.test.in/audio_ivrs/sr_listenglishMSTR001.wav"});
values.push({"kannada":"http://www.test.in/audio_ivrs/sr_listfrenchMSTR001.wav"});
This would tell me that you're pushing objects into an array which is perfectly valid JavaScript.
To get this information from the array into the structure you need you can use something like this loop:
var out = {
urlList: {}
};
for (var i = 0, l = values.length; i < l; i++) {
var el = values[i];
var key = Object.keys(el);
var value = el[key];
out.urlList[key] = value;
}
JSON.stringify(out);
DEMO

Push an object into the object list object

The simplest question ever, and I did not find right answer yet.
Got object list: object_list = {}
Got object: object_x = {...}
How do I add object_x to object_list[objects_x]?
I tried: object_list[objects_x][object_list[objects_x].length] = object_x, but object_list[objects_x].length is undefined.
push() does not work either.
Do I really need to define external counter for that?
PLEASE NOT THAT I MEAN LIST OF LISTS OF OBJECTS. NOTE THE DIFFERENCE BETWEEN objects_x and object_x.
There is no simple solution like in PHP where you simply $array['something'][] = $somedata ?

object_list['object_x'] = object_x;
// or
object_list.object_x = object_x;
console.log(object_list.object_x === object_list['object_x'])
How to work with objects - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Working_with_Objects

When you create a variable like var stuff = {}, you're creating an empty object literal, it has no attributes (properties or methods) other than what it inherits from Object. If you want to keep objects stored in various lists in this object you need to first create those lists.
var stuff = { shelves: [], selectors: [], images: [], additional: [] };
Now you can add whatever you want to those lists as much as you want.
var image = { src: '/path/to/image.jpg' };
stuff.images.push(image);
You can add more lists to stuff whenever like by just setting the new property on stuff.
stuff.some_other_list = []
Hope it helps.

Your base assumption is wrong.
This:
var object_list = {}
Is not a list. It's not an array and you can't reference its items by index, thus it also does not have .length property.
What you are after is a plain array:
var object_list = [];
Now you can push items into it:
object_list.push(object_x);
Edit: based on your comments and edits, I think what you're really after are couple of helper functions:
function AddToList(list, item) {
var counter = 0;
for (var key in list)
counter++;
var key = "item_index_" + counter;
list[key] = item;
}
function GetItemByIndex(list, index) {
var counter = 0;
var existingKey = "";
for (var key in list) {
if (counter == index) {
existingKey = key;
break;
}
counter++;
}
return (existingKey.toString().length > 0) ? list[existingKey] : null;
}
Having those, you can have such a code now:
var mainList = {};
var newItem = { "foo": "bar" };
AddToList(mainList, newItem);
var dummy = GetItemByIndex(mainList, 0)["foo"]; //will contain "bar"
Live test case.

If you are interested use object, not array, you can use like this:
var object_list = {};
var object_x = {'prop1':'val1'};
// add object
object_list.myobj = object_x;
// for access, same scheme.
object_list.myobj.prop1 = 'valX';
// for loop thru
for (var key in object_list) {
var obj = object_list[key];
obj.prop1 = 'valY';
}

Declaring array of objects

I have a variable which is an array and I want every element of the array to act as an object by default. To achieve this, I can do something like this in my code.
var sample = new Array();
sample[0] = new Object();
sample[1] = new Object();
This works fine, but I don't want to mention any index number. I want all elements of my array to be an object. How do I declare or initialize it?
var sample = new Array();
sample[] = new Object();
I tried the above code but it doesn't work. How do I initialize an array of objects without using an index number?

Use array.push() to add an item to the end of the array.
var sample = new Array();
sample.push(new Object());
To do this n times use a for loop.
var n = 100;
var sample = new Array();
for (var i = 0; i < n; i++)
sample.push(new Object());
Note that you can also substitute new Array() with [] and new Object() with {} so it becomes:
var n = 100;
var sample = [];
for (var i = 0; i < n; i++)
sample.push({});

Depending on what you mean by declaring, you can try using object literals in an array literal:
var sample = [{}, {}, {} /*, ... */];
EDIT: If your goal is an array whose undefined items are empty object literals by default, you can write a small utility function:
function getDefaultObjectAt(array, index)
{
return array[index] = array[index] || {};
}
Then use it like this:
var sample = [];
var obj = getDefaultObjectAt(sample, 0); // {} returned and stored at index 0.
Or even:
getDefaultObjectAt(sample, 1).prop = "val"; // { prop: "val" } stored at index 1.
Of course, direct assignment to the return value of getDefaultObjectAt() will not work, so you cannot write:
getDefaultObjectAt(sample, 2) = { prop: "val" };

You can use fill().
let arr = new Array(5).fill('lol');
let arr2 = new Array(5).fill({ test: 'a' });
// or if you want different objects
let arr3 = new Array(5).fill().map((_, i) => ({ id: i }));
Will create an array of 5 items. Then you can use forEach for example.
arr.forEach(str => console.log(str));
Note that when doing new Array(5) it's just an object with length 5 and the array is empty. When you use fill() you fill each individual spot with whatever you want.

After seeing how you responded in the comments. It seems like it would be best to use push as others have suggested. This way you don't need to know the indices, but you can still add to the array.
var arr = [];
function funcInJsFile() {
// Do Stuff
var obj = {x: 54, y: 10};
arr.push(obj);
}
In this case, every time you use that function, it will push a new object into the array.

You don't really need to create blank Objects ever. You can't do anything with them. Just add your working objects to the sample as needed. Use push as Daniel Imms suggested, and use literals as Frédéric Hamidi suggested. You seem to want to program Javascript like C.
var samples = []; /* If you have no data to put in yet. */
/* Later, probably in a callback method with computed data */
/* replacing the constants. */
samples.push(new Sample(1, 2, 3)); /* Assuming Sample is an object. */
/* or */
samples.push({id: 23, chemical: "NO2", ppm: 1.4}); /* Object literal. */
I believe using new Array(10) creates an array with 10 undefined elements.

You can instantiate an array of "object type" in one line like this (just replace new Object() with your object):
var elements = 1000;
var MyArray = Array.apply(null, Array(elements)).map(function () { return new Object(); });

Well array.length should do the trick or not? something like, i mean you don't need to know the index range if you just read it..
var arrayContainingObjects = [];
for (var i = 0; i < arrayContainingYourItems.length; i++){
arrayContainingObjects.push {(property: arrayContainingYourItems[i])};
}
Maybe i didn't understand your Question correctly, but you should be able to get the length of your Array this way and transforming them into objects. Daniel kind of gave the same answer to be honest. You could just save your array-length in to his variable and it would be done.
IF and this should not happen in my opinion you can't get your Array-length. As you said w/o getting the index number you could do it like this:
var arrayContainingObjects = [];
for (;;){
try{
arrayContainingObjects.push {(property: arrayContainingYourItems[i])};
}
}
catch(err){
break;
}
It is the not-nice version of the one above but the loop would execute until you "run" out of the index range.

//making array of book object
var books = [];
var new_book = {id: "book1", name: "twilight", category: "Movies", price: 10};
books.push(new_book);
new_book = {id: "book2", name: "The_call", category: "Movies", price: 17};
books.push(new_book);
console.log(books[0].id);
console.log(books[0].name);
console.log(books[0].category);
console.log(books[0].price);
// also we have array of albums
var albums = []
var new_album = {id: "album1", name: "Ahla w Ahla", category: "Music", price: 15};
albums.push(new_album);
new_album = {id: "album2", name: "El-leila", category: "Music", price: 29};
albums.push(new_album);
//Now, content [0] contains all books & content[1] contains all albums
var content = [];
content.push(books);
content.push(albums);
var my_books = content[0];
var my_albums = content[1];
console.log(my_books[0].name);
console.log(my_books[1].name);
console.log(my_albums[0].name);
console.log(my_albums[1].name);
This Example Works with me.
Snapshot for the Output on Browser Console

Try this-
var arr = [];
arr.push({});

const sample = [];
list.forEach(element => {
const item = {} as { name: string, description: string };
item.name= element.name;
item.description= element.description;
sample.push(item);
});
return sample;
Anyone try this.. and suggest something.

Use array.push() to add an item to the end of the array.
var sample = new Array();
sample.push(new Object());
you can use it
var x = 100;
var sample = [];
for(let i=0; i<x ;i++){
sample.push({})
OR
sample.push(new Object())
}

Using forEach we can store data in case we have already data we want to do some business login on data.
var sample = new Array();
var x = 10;
var sample = [1,2,3,4,5,6,7,8,9];
var data = [];
sample.forEach(function(item){
data.push(item);
})
document.write(data);
Example by using simple for loop
var data = [];
for(var i = 0 ; i < 10 ; i++){
data.push(i);
}
document.write(data);

If you want all elements inside an array to be objects, you can use of JavaScript Proxy to apply a validation on objects before you insert them in an array. It's quite simple,
const arr = new Proxy(new Array(), {
set(target, key, value) {
if ((value !== null && typeof value === 'object') || key === 'length') {
return Reflect.set(...arguments);
} else {
throw new Error('Only objects are allowed');
}
}
});
Now if you try to do something like this:
arr[0] = 'Hello World'; // Error
It will throw an error. However if you insert an object, it will be allowed:
arr[0] = {}; // Allowed
For more details on Proxies please refer to this link:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy
If you are looking for a polyfill implementation you can checkout this link:
https://github.com/GoogleChrome/proxy-polyfill

The below code from my project maybe it good for you
reCalculateDetailSummary(updateMode: boolean) {
var summaryList: any = [];
var list: any;
if (updateMode) { list = this.state.pageParams.data.chargeDefinitionList }
else {
list = this.state.chargeDefinitionList;
}
list.forEach((item: any) => {
if (summaryList == null || summaryList.length == 0) {
var obj = {
chargeClassification: item.classfication,
totalChargeAmount: item.chargeAmount
};
summaryList.push(obj);
} else {
if (summaryList.find((x: any) => x.chargeClassification == item.classfication)) {
summaryList.find((x: any) => x.chargeClassification == item.classfication)
.totalChargeAmount += item.chargeAmount;
}
}
});
if (summaryList != null && summaryList.length != 0) {
summaryList.push({
chargeClassification: 'Total',
totalChargeAmount: summaryList.reduce((a: any, b: any) => a + b).totalChargeAmount
})
}
this.setState({ detailSummaryList: summaryList });
}

var ArrayofObjects = [{}]; //An empty array of objects.

Can't reference array by index

I have an array defined as:
var subjectCache = [];
I then have some code to build it up, which is working ok.
However, if I try to reference the array by an index, e.g.:
var x = subjectCache[0];
or
var x = subjectCache[1];
I get undefined.
Also subjectCache.length is always 0 (zero).
if I try to reference it by its key, e.g.:
var x = subjectCache['12345'];
it works.
Is this normal? Shouldn't I be able to reference it by its index whatever?
I'm using Internet Explorer, if it makes a difference (and it probably does :( )
[Edit]
this is the code I'm using to build the array, although I really don't think it is to blame.
It's a callback from a webservice call. This is working fine and the array is being populated.
var subjectCache = [];
var subjectCacheCount = 0;
function refreshSubjectsCallback(data) {
// update subjects
// loop through retrieved subjects and add to cache
for( i=0; i < data.length; i++ )
{
var subject = data[i];
var subjectid = subject.SubjectId;
subjectCache[subjectid] = subject;
subjectCacheCount += 1;
}
}
[/Edit]

You're probably assigning keys manually instead of using subjectCache.push() to add new elements to the array:
var array = [];
array['foo'] = 'bar';
console.log(array.length); // 0
The length attribute isn't going to reflect those changes the way you'd expect:
> var a = [];
undefined
> a[100] = 2; // The previous `100` entries evaluate to `undefined`
2
> a.length;
101
Instead, use an object:
var object = {};
object['foo'] = 'bar';
for (var key in object) {
var value = object[key];
console.log(value);
}

From your symptoms, it sounds like you are trying to treat the array as an associative array.
In Javascript, arrays work like this:
var a = [];
a[1] = 10;
alert(a.length);
Objects work like this:
var o = {};
o.myProp = true;
o["myOtherProp"] = false;

Arrays only work with numeric keys not strings. Strings assign properties to the object, and aren't counted as part of length nor it's numeric indices.
When building the array, make sure you are assigning to a numeric position within the array.

No, it will not work, because you haven't created arrays but objects.
you will have to access it by its key.
var x = subjectCache['12345'];
If this works and subjectCache.length doesn't, I think you are making an object not an array. You are confused.

Somewhere along the road you lost the array, and the variable subjectCache points to a different kind of object.
If it was an array, it can't have the length zero and contain an item that is reachable using subjectCache['12345']. When you access an item in an array it doesn't make any difference if you use a numeric index or a string representing a number.

Another javascript array challenge

Solving another array manipulation, and I'm taking longer than usual to solve this. I need help in combining array values:
var array1 = ["alpha|LJ", "bravo|MH", "charlie|MH", "delta|MF",
"echo|16", "{foxtrot}|GG", "{golf}|HS"];
var array2 = ["charlie-{golf}-{foxtrot}", "echo-{golf}"]; //some templates
such that the final array be:
final_array = ["alpha-LJ", "bravo-MH", "charlie-HS-GG-MH", "delta-MF",
"echo-HS-16"];
To make it clear how I arrived with the final_array, alpha, bravo and delta only got their "|" replaced with "-" since they are not found on my array2 template. charlie and echo got the template so the respective values of the {} were replaced based on array1. Array1 honestly is not the best key:value relationship that I could come up for now.
Here are some requirementL:
* Anything in array1 with {} braces are not meant to be templated.
* Keywords in array2 will always have a matching value in array1.
I've read about jquery .map() and thinking that it is achievable using this, maybe together with Regexp. Hope you'll utilize these. Also, if it helps, final_array can be of any order.
I really need to up my knowledge on these two topics... :|
Thank you in advance.

Edit: Updated to match your output and comment some of the madness. This doesn't feel like it's the most efficient, given the split() done to values at the start and then again at the end...but it works.
function funkyTransform( values, templates ){
// Make a copy of the array we were given so we can mutate it
// without rudely changing something passed to our function.
var result = values.concat();
// Map {value} entries for later lookup, and throw them out of the result
var valueMap = {};
for (var i=result.length-1;i>=0;--i){
var pair = result[i].split('|');
if (pair[0][0]=="{"){
valueMap[pair[0]] = pair[1];
result.splice(i,1); // Yank this from the result
}
}
console.log(valueMap);
// {
// "{foxtrot}": "GG",
// "{golf}": "HS"
// }
// Use the value map to replace text in our "templates", and
// create a map from the first part of the template to the rest.
// THIS SHOULD REALLY SCAN THE TEMPLATE FOR "{...}" PIECES
// AND LOOK THEM UP IN THE MAP; OOPS O(N^2)
var templateMap = {};
for (var i=templates.length-1;i>=0;--i){
var template = templates[i];
for (var name in valueMap){
if (valueMap.hasOwnProperty(name)){
template = template.replace(name,valueMap[name]);
}
}
var templateName = template.split('-')[0];
templateMap[ templateName ] = template.slice(templateName.length+1);
}
console.log(templateMap);
// {
// "charlie": "HS-GG",
// "echo": "HS"
// }
// Go through the results again, replacing template text from the templateMap
for (var i=result.length-1;i>=0;--i){
var pieces = result[i].split('|');
var template = templateMap[pieces[0]];
if (template) pieces.splice(1,0,template);
result[i] = pieces.join('-');
}
return result;
}
var output = funkyTransform( array1, array2 );
console.log(output);
// ["alpha-LJ", "bravo-MH", "charlie-HS-GG-MH", "delta-MF", "echo-HS-16"]

This managed to get your desired output, though I made a few assumptions:
Anything in array1 with {} braces are not meant to be templated.
Keywords in array2 will always have a matching value in array1 (this can easily be changed, but not sure what your rule would be).
Code:
// This is the main code
var final_array = $.map(array1, function (item) {
var components = item.split('|');
// Ignore elements between {} braces
if (/^\{.*\}$/.test(components[0])) return;
components[0] = template(components[0]);
return components.join('-');
});
// Helper to lookup array2 for a particular string and template it
// with the values from array1
function template(str) {
var index = indexOfMatching(array2, str, '-');
if (index == -1) return str;
var components = array2[index].split('-');
var result = [str];
for (var i = 1; i < components.length; i++) {
result.push(array1[indexOfMatching(array1, components[i], '|')]
.split('|')[1]);
}
return result.join('-');
}
// Helper to for looking up array1 and array2
function indexOfMatching(array, target, separator) {
for (var i = 0; i < array.length; i++) {
if (array[i].split(separator)[0] === target) return i;
}
return -1;
}