cannot iterate through array and change value in JS - javascript

I have to iterate through an array, change one of its values, and create another array refelecting the changes.
this is what I have so far:
JS:
var arr = new Array();
arr['t1'] = "sdfsdf";
arr['t2'] = "sdfsdf";
arr['t3'] = "sdfsdf";
arr['t4'] = "sdfsdf";
arr['t5'] = "sdfsdf";
var last = new Array();
for (var i = 0; i <= 5; i++) {
arr['t2'] = i;
last.push(arr);
}
console.log(last);
Unfortunately, these are my results
As you can see, I am not getting the results needed as 0,1,2.. instead I am getting 2, 2, 2..
This is what i would like my results to be:
How can I fix this?

You have to make a copy, otherwise you are dealing with reference to the same object all the time. As it was said before - javascript does not have associate arrays, only objects with properties.
var arr = {}; // empty object
arr['t1'] = "sdfsdf";
arr['t2'] = "sdfsdf";
arr['t3'] = "sdfsdf";
arr['t4'] = "sdfsdf";
arr['t5'] = "sdfsdf";
var last = new Array();
for (var i = 0; i <= 5; i++) {
var copy = JSON.parse(JSON.stringify(arr)); //create a copy, one of the ways
copy['t2'] = i; // set value of its element
last.push(copy); // push copy into last
}
console.log(last);
ps: you can use dot notation arr.t1 instead of arr['t1']

The array access with ['t2'] is not the problem. This is a regular JavaScript feature.
The problem is: You are adding the SAME array to "last" (5 times in code, 3 times in the screenshot).
Every time you set ['t2'] = i, you will change the values in "last" also, because they are actually just references to the same array-instance.
You must create a copy/clone of the array before you add it to "last".
This is what will happen in all languages where arrays are references to objects (Java, C#...). It would work with C++ STL though.

Related

How can I add values from existing object to new object dynamically?

Currently, I have an empty new object and I want to populate values from an existing object to new object because I want to use an object with only limited properties from the existing object (e.g. I only want the four properties instead of eight).
Here's how I am doing the mapping so far:
const newObject: any = {};
for (let i = 0; i < this.PRODUCT_DATA.length; i++) {
newObject._productSkuKey = this.PRODUCT_DATA[i]._productSkuKey;
newObject._storeKey = this.itemPriceForm.get('location').value;
newObject._price = this.PRODUCT_DATA[i]._price;
newObject._status = this.PRODUCT_DATA[i]._isActive;
this.updatedProducts.push(newObject);
}
So far, it looks to be storing the values from the existing object to newObject. However, it is only saving the last object values and not the different values from the object. How can I fix this to save all values (not just the last values for every object in the array)?
You need to make a copy of that before pushing in array
const newObject: any = {};
for (let i = 0; i < this.PRODUCT_DATA.length; i++) {
newObject._productSkuKey = this.PRODUCT_DATA[i]._productSkuKey;
newObject._storeKey = this.itemPriceForm.get('location').value;
newObject._price = this.PRODUCT_DATA[i]._price;
newObject._status = this.PRODUCT_DATA[i]._isActive;
this.updatedProducts.push(Object.assign({}, newObject));
// Or
// this.updatedProducts.push({ ...newObjec });
}
Or Simply create object inside loop. I love to use Array.prototype.forEach and Array.prototype.map
this.updatedProducts = this.PRODUCT_DATA.map(({_productSkuKey, _price, _isActive})=> ({
_productSkuKey,
_storeKey: this.itemPriceForm.get('location').value,
_price,
_status: _isActive
});
Avoid declaring newObject as 'const'. This is an updated code that works for me.
//avoid using a const, as you cannot override it
let newObject: any = {};
for (let i = 0; i < this.PRODUCT_DATA.length; i++) {
newObject._productSkuKey = this.PRODUCT_DATA[i]._productSkuKey;
newObject._storeKey = this.itemPriceForm.get('location').value;
newObject._price = this.PRODUCT_DATA[i]._price;
newObject._status = this.PRODUCT_DATA[i]._isActive;
this.updatedProducts.push(newObject);
//after pushing the object, empty all the current contents
newObject={};
}

Advice on the best way to collect values in an array

I need to save all the color values ​​of the elements in the pages of my site and put them in a database. I thought I'd do it this way:
First thing I'm going to pick up the rgb values ​​of each element so
$("*").each(function(e){
createColorArray($(this).css('backgroundColor'));
});
then in the function createColorArray store into an array all the values ​​that are passed
function createColorArray(rgbColor)
{
//Create rgb array
}
and finally remove duplicate items from my array
function removeDoupe(ar) {
var temp = {};
for (var i = 0; i < ar.length; i++)
temp[ar[i]] = true;
var r = [];
for (var k in temp)
r.push(k);
return r;
}
now my question is,
how recommended to create the array? directly inside the $ ("*") or in a dedicated function as I'm thinking? also i need than once removed duplicates in the new array "clean" as well as the rgb value I would have also given the number of times that value was in the original.
Some example code?
As I mentioned in the comments, why not check for duplicates earlier? A simple example:
var colors = [];
$('*').each(function(i, el){
var $element = $(el),
color = $element.css('background-color');
if(!~$.inArray(color, colors))
colors.push(color);
});
console.log(colors);
http://jsfiddle.net/sL9oeywk/
The best way to do this is to do it all while you are working on it. Heres a way you could potentially do it:
var colors = new Array();
var tempColors = {};
$(".colors").each(function(){
var c = $(this).val();
// check if the color exists without looping
if(typeof tempColors[c] == "undefined"){
// if it doesn't, add it to both variables.
tempColors[c] = true;
colors.push(c);
}
});
This will result in two variables: one is an object that you don't have to loop through to find out if you defined it before, one is a colors array that you push to using standard javascript.
You shouldn't make it a dedicated function if you are not reusing it, but you could make it an object like this:
var colors = function(){
var self = this;
self.array = new Array();
// this is a dedicated check function so we don't need separate variables.
// returns true if the color exists, false otherwise
self.check = function(color){
for(var i =0; i < self.array.length; i++){
if(self.array[i] === color) return true;
}
return false;
}
self.add = function(color){
// use the check function, if it returns false, the color does not exist yet.
if(!self.check(color)){
self.array.push(c);
}
}
}
You can then instantiate a colorlist using var colorlist = new colors(); and add colors using colorlist.add("dd0300"). Accessing the array can be done by requesting colorlist.array.

very simple, javascript arrays syntax

I have a very simple JS Arrays question, my simple canvas game has been behaving differently when I replaced one block of code with another. Could you look them over and see why they are functionally different from one another, and maybe provide a suggestion? I may need these arrays to have 20+ items so I'm looking for a more condensed style.
There's this one, which is short enough for me to work with, but doesn't run well:
var srd=new Array(1,1,1);
var sw=new Array(0,0,0);
var sang=new Array(0,0,0);
var sHealth=new Array(20,20,20);
And then there's the original one, which is longer but works fine:
var srd = new Array();
srd[1] = 1;
srd[2] = 1;
srd[3] = 1;
var sw = new Array();
sw[1] =0;
sw[2] =0;
sw[3] =0;
var sang = new Array();
sang[1] = 0;
sang[2] = 0;
sang[3] = 0;
var sHealth = new Array();
sHealth[1] = 20;
sHealth[2] = 20;
sHealth[3] = 20;
Arrays are zero-indexed in JavaScript. The first element is 0, not 1:
var srd = new Array();
srd[0] = 1;
srd[1] = 1;
srd[2] = 1;
Also, you may want to use the more common array constructor:
var srd = [1, 1, 1];
I have a feeling that you may be assuming that the first element is 1 instead of 0, which is why the first version doesn't work while the second one does.
You should do this....in Arrays values are stored as such that first one is at 0 and so on.
so 1st value will be accessed as this...
var x = abc[0]; //first value of array abc being assigned to x.
Do this (you see i actually read your question and this is what you like)
var srd=['',1,1,1];
var sw=['',0,0,0];
var sang=['',0,0,0];
var sHealth=['',20,20,20];
you can declare an array(object) in javascript like this
var x = []; -------------Literal - its a shortcut provided by JS to quickly declare something as an Array.
var x = new Array; --Array constructor
Things to look up regarding
literal
object literal
proto
word new
function object
function property prototype
You can also do these:
var x=1,y=2,
z=3,
f;
var b = something || {}; \\become a copy of object called something if it's not there then become an empty object.
It looks like one starts the arrays at index 0 and the other one starts at index 1
It depends on your implementation, but it's likely because of arrays being 0-indexed. In your first block of code, each number is offset by one index spot from the second block. The first one is equivalent to:
var srd = new Array();
srd[0] = 1;
srd[1] = 1;
srd[2] = 1;
in the way you wrote it for the second block.

How to split a URL string with parameters into an array using JavaScript

I'm trying to break up a string like this one:
fname=bill&mname=&lname=jones&addr1=This%20House&...
I want to end up with an array indexed like this
myarray[0][0] = fname
myarray[0][1] = bill
myarray[1][0] = mname
myarray[1][1] =
myarray[2][0] = lname
myarray[2][1] = jones
myarray[3][0] = addr
myarray[3][1] = This House
The url is quite a bit longer than the example. This is what I've tried:
var
fArray = [],
nv = [],
myarray = [];
fArray = fields.split('&');
// split it into fArray[i]['name']="value"
for (i=0; i < fArray.length; i++) {
nv = fArray[i].split('=');
myarray.push(nv[0],nv[1]);
nv.length = 0;
}
The final product is intended to be in 'myarray' and it is, except that I'm getting a one dimensional array instead of a 2 dimensional one.
The next process is intended to search for (for example) 'lname' and returning the index of it, so that if it returned '3' I can then access the actual last name with myarray[3][1].
Does this make sense or am I over complicating things?
Your line myarray.push(nv[0],nv[1]); pushes two elements to the array myarray, not a single cell with two elements as you expect (ref: array.push). What you want is myarray.push( [nv[0],nv[1]] ) (note the brackets), or myarray.push(nv.slice(0, 2)) (ref: array.slice).
To simplify your code, may I suggest using Array.map:
var q = "foo=bar&baz=quux&lorem=ipsum";
// PS. If you're parsing from a-tag nodes, they have a property
// node.search which contains the query string, but note that
// it has a leading ? so you want node.search.substr(1)
var vars = q.split("&").map(function (kv) {
return kv.split("=", 2);
});
For searching, I would suggest using array.filter:
var srchkey = "foo";
var matches = vars.filter(function (v) { return v[0] === srchkey; });
NB. array.filter will always return an array. If you always want just a single value, you could use array.some or a bespoke searching algorithm.
for (var i = 0; i < fArray.length; i++) {
nv = fArray[i].split('=');
myarray.push([nv[0],nv[1]]);
}
nv.length = 0; is not required, since you're setting nv in each iteration of the for loop.
Also, use var i in the for-loop, otherwise, you're using / assigning a global variable i, that's asking for interference.

javascript how to find number of children in an object

is there a way to find the number of children in a javascript object other than running a loop and using a counter? I can leverage jquery if it will help. I am doing this:
var childScenesObj = [];
var childScenesLen = scenes[sceneID].length; //need to find number of children of scenes[sceneID]. This obviously does not work, as it an object, not an array.
for (childIndex in scenes[sceneID].children) {
childSceneObj = new Object();
childSceneID = scenes[sceneID].children[childIndex];
childSceneNode = scenes[childSceneID];
childSceneObj.name = childSceneNode.name;
childSceneObj.id = childSceneID;
childScenesObj .push(childSceneObj);
}
The following works in ECMAScript5 (Javascript 1.85)
var x = {"1":1, "A":2};
Object.keys(x).length; //outputs 2
If that object is actually an Array, .length will always get you the number of indexes. If you're referring to an object and you want to get the number of attributes/keys in the object, there's no way I know to that other than a counter:
var myArr = [];
alert(myArr.length);// 0
myArr.push('hi');
alert(myArr.length);// 1
var myObj = {};
myObj["color1"] = "red";
myObj["color2"] = "blue";
// only way I know of to get "myObj.length"
var myObjLen = 0;
for(var key in myObj)
myObjLen++;

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