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javascript variable changing value after changes in original variable

I am having trouble maintaining the original value of a variable after making new changes to the original variable.
Code:
(...)
data = Illumination.calculate_N(data)
data = Illumination.calculate_pi(data)
data = Illumination.calculate_kwh(data)
data = Illumination.calculate_ca(data)
let data_base = data
let ca_base = data.ca
let kwh_base = data.kwh
let pi_base = data.pi
(...)
data = Illumination.calculate_N(data)
data = Illumination.calculate_pi(data)
data = Illumination.calculate_kwh(data)
data = Illumination.calculate_ca(data)
let data_proposto = data
let ca_proposto = data.ca
let kwh_proposto = data.kwh
let pi_proposto = data.pi
-----------------------------------
EXAMPLE:
static calculate_ai(data){
data.ai = data.areaTotal*data.au
return data
}
It was expected that the original variable (date) would have its values ​​changed, and this happens correctly, however, the variables data_base and data_proposto are not keeping their values
Both variables at the end of the calculation have the same values ​​as the variable date
The variables ca_proposto, ca_base, and the like store their values ​​correctly
Any idea?
The only interactions of the variables data_base and data_proposto were their creations with the data variable and their return of the function
OBS: If I use console.log () to view the value of the data_base variable before redoing the new calculations (Illumination.calculate_N (data)), the value of the variable appears correctly as it should, it is changed shortly after these calculations.

Because in both cases you are assigning not the object itself in the current state, but a reference to that object. What you need to do is to clone the object so the state is frozen at that point.
Simple Clone (Shallow Copy)
let data_base = Object.assign({}, data); //you get a clone of data
let data_proposto = Object.assign({}, data);
The limitation here is that it only does a shallow copy. See Deep Copy below for further explanation.
JSON Clone
This is a quick-and-dirty way to clone as it converts a JSON object to a string, and then back. i.e. you are no longer getting a reference, but a new object.
let data_base = JSON.parse(JSON.stringify(data));
let data_postero = JSON.parse(JSON.stringify(data));
But this won't work if your object is not JSON-safe.
Deep Copy
The least elegant method is probably safest. It deep copies the properties over into a new object. The key difference with Object.assign() is that it copies the values of nested properties, whereas Object.assign() copies the reference to nested objects.
So with Object.assign() any subsequent changes in your nested objects will affect all versions of your "clones". This won't happen if your clones only have property values of those nested objects at the time of cloning – these values are not affected by any changes to the nested objects.
const deepCopy = function(src) {
let target = {};
// using for/in on object also returns prototype properties
for (let prop in src) {
// .hasOwnProperty() filters out these prototype properties.
if (src.hasOwnProperty(prop)) {
target[prop] = src[prop]; //iteratively copies over values, not references
}
}
return target;
}
let data_base = deepCopy(data);
let data_postero = deepCopy(data);

#chatnoir Defined the problem very well, But I do not agree with his JSON serialization solution due to the below probleam:
You will lose any Javascript property that has no equivalent type in
JSON, like Function or Infinity. Any property that’s assigned to
undefined will be ignored by JSON.stringify, causing them to be missed
on the cloned object.
My suggestion to perform deep copy is to rely on a library that’s well
tested, very popular and carefully maintained: Lodash.
Lodash offers the very convenient clone and deepclone functions to perform shallow and deep cloning.
Lodash has this nice feature: you can import single functions separately in your project to reduce a lot the size of the dependency.
Please find the running sample code here: https://glitch.com/edit/#!/flavio-lodash-clone-shallow-deep?path=server.js:1:0

You are using the same variable data inside and outside functions.
ie; data is in the global scope.
static calculate_ai(data){
data.ai = data.areaTotal*data.au
return data
}
even though you are expecting the scope of the variable data inside the method calculate_ai to be limited to that method, it is not the case. data is in global scope and therefore, the value changes inside the method for the variable affects outside as well.
An effective solution is to use a different variable inside the method.

A variable is like an octopus tentacle, and not as a box (as it’s commonly described). In this analogy, the variable's name can be thought of as the name of a tentacle.
A variable (tentacle) holds on to a value in what’s called a binding. A binding is an association of a variable to a value: x = 1.
In JavaScript, if a variable b holds on to variable a, changing the value to which variable a holds onto, will change the value to which variable b holds onto, as b and a are referencing to the same value:
let a = {key: 1}
let b = a
console.log(`a: ${a.key}`) // -> 1
console.log(`b: ${b.key}`) // -> 1
a.key = 2
console.log(`a: ${a.key}`) // -> 2
console.log(`b: ${b.key}`) // -> 2
a = {key: 3} // This will point variable 'a' to a new object, while variable 'b' still points to the original object.
console.log(`a: ${a.key}`) // -> 3
console.log(`b: ${b.key}`) // -> 2

New objects get overwritten when being added to an array

Newbie here...be nice.
I have an empty object that will get pushed into an array.
listView = {};
I add properties to it.
listView.code = code;
listView.description = description;
I push the results object into an array.
listy.push(listView);
Each time I enter a new selection in step #2 it overwrites the object instead of adding the new object properties to the array. It also increments the index by one, so it just repeats...
[{"code":"I77.812","description":"Thoracoabdominal Aortic Ectasia"}]
[{"code":"I77.811","description":"Abdominal Aortic Ectasia"},{"code":"I77.811","description":"Abdominal Aortic Ectasia"}]
[{"code":"I06.1","description":"Rheumatic aortic insufficiency"},{"code":"I06.1","description":"Rheumatic aortic insufficiency"},{"code":"I06.1","description":"Rheumatic aortic insufficiency"}]
The array should contain three different objects. But instead it has three copies of the newly added one...
How should I be adding the new choice objects so that they don't get overwritten?

You are always adding a reference to the same object, and changing that same object, instead of adding new objects. See this:
var a = [];
var o = {};
for (var i = 0; i < 5; i++) {
o.id = i;
a.push(o);
}
a
// => [{"id":4},{"id":4},{"id":4},{"id":4},{"id":4}]
But
var a = [];
for (var i = 0; i < 5; i++) {
var o = {};
o.id = i;
a.push(o);
}
a
// => [{"id":0},{"id":1},{"id":2},{"id":3},{"id":4}]
The difference is, the second code always makes a new object that is distinct from all other objects already in the array.
As a metaphor, imagine a theatre director in casting. He turns to an actor, says "You... you'll be Romeo.". Then he looks at the same actor, says "You... you'll be Mercutio. Here, Mercutio, take this sword. Romeo... who told you to get a sword?!?" completely failing to realise that, if Romeo and Mercutio are the same person, if one of them picks up a sword, the other does it too.

Seeing as you declared yourself a 'newbie' i figured i'd take a bit more time explaining. When you push an object to an array, you don't copy the object. You just tell the array where to find the object (a reference). If you push the same object 3 times, the array just has 3 indexes at which it finds the same object. There's several ways around this, the easiest being that you declare the variable inside the loop
for (var i=0;i<3;i++){
var listView = {};
listView.id = i;
listy.push(listView);
}
This way listView is a different reference each time. The other way is to create a new object when you push
listy.push({id:listView.id, description:listView.description});
which works because simple variables are 'copied' into the array and not referenced.

your assignment of the properties of an object are simply replacing the existing properties. wh en you push the object in the array by name, you are push a reference to the object and not a value. This is why all the elements in the array are the same. You need to create a new object every time you push. Something like this should work for you.
listy.push({code:code, description:description});

try this :
listy.push({
code:listView.code,
description : listView.description
})
In my code I have used pass by value.
In your code , you are using Objects which are passed by reference .
You are adding same reference again and again so at the end you will get an array having all the values of same object .
To understand more about pass by value and pass by reference you can reffer this link :
Pass Variables by Reference in Javascript

Copying an array of objects into another array in javascript (Deep Copy)

Copying an array of objects into another array in javascript using slice(0) and concat() doesnt work.
I have tried the following to test if i get the expected behaviour of deep copy using this. But the original array is also getting modified after i make changes in the copied array.
var tags = [];
for(var i=0; i<3; i++) {
tags.push({
sortOrder: i,
type: 'miss'
})
}
for(var tag in tags) {
if(tags[tag].sortOrder == 1) {
tags[tag].type = 'done'
}
}
console.dir(tags)
var copy = tags.slice(0)
console.dir(copy)
copy[0].type = 'test'
console.dir(tags)
var another = tags.concat()
another[0].type = 'miss'
console.dir(tags)
How can i do a deep copy of a array into another, so that the original array is not modified if i make a change in copy array.

Try
var copy = JSON.parse(JSON.stringify(tags));

Try the following
// Deep copy
var newArray = jQuery.extend(true, [], oldArray);
For more details check this question out What is the most efficient way to deep clone an object in JavaScript?

As mentioned Here .slice(0) will be effective in cloning the array with primitive type elements. However in your example tags array contains anonymous objects. Hence any changes to these objects in cloned array are reflected in tags array.
#dangh's reply above derefences these element objects and create new ones.
Here is another thread addressing similar situation

A nice way to clone an array of objects with ES6 is to use spread syntax:
const clonedArray = [...oldArray];
MDN

Easiest and the optimistic way of doing this in one single line is using Underscore/Lodash
let a = _.map(b, _.clone)

You just need to use the '...' notation.
// THE FOLLOWING LINE COPIES all elements of 'tags' INTO 'copy'
var copy = [...tags]
When you have an array say x, [...x] creates a new array with all the values of x. Be careful because this notation works slightly differently on objects. It splits the objects into all of its key, value pairs. So if you want to pass all the key value pairs of an object into a function you just need to pass function({...obj})

Same issue happen to me. I have data from service and save to another variable. When ever I update my array the copied array also updated. old code is like below
//$scope.MyData get from service
$scope.MyDataOriginal = $scope.MyData;
So when ever I change $scope.MyData also change $scope.MyDataOriginal.
I found a solution that angular.copy right code as below
$scope.MyDataOriginal = angular.copy($scope.MyData);

I know that this is a bit older post but I had the good fortune to have found a decent way to deep copy arrays, even those containing arrays, and objects, and even objects containing arrays are copied... I only can see one issue with this code is if you don't have enough memory I can see this choking on very large arrays of arrays and objects... But for the most part it should work. The reason that I am posting this here is that it accomplishes the OP request to copy array of objects by value and not by reference... so now with the code (the checks are from SO, the main copy function I wrote myself, not that some one else probably hasn't written before, I am just not aware of them)::
var isArray = function(a){return (!!a) && (a.constructor===Array);}
var isObject = function(a){return (!!a) && (a.constructor===Object);}
Array.prototype.copy = function(){
var newvals=[],
self=this;
for(var i = 0;i < self.length;i++){
var e=self[i];
if(isObject(e)){
var tmp={},
oKeys=Object.keys(e);
for(var x = 0;x < oKeys.length;x++){
var oks=oKeys[x];
if(isArray(e[oks])){
tmp[oks]=e[oks].copy();
} else {
tmp[oks]=e[oks];
}
}
newvals.push(tmp);
} else {
if(isArray(e)){
newvals.push(e.copy());
} else {
newvals.push(e);
}
}
}
return newvals;
}
This function (Array.prototype.copy) uses recursion to recall it self when an object or array is called returning the values as needed. The process is decently speedy, and does exactly what you would want it to do, it does a deep copy of an array, by value... Tested in chrome, and IE11 and it works in these two browsers.

The way to deeply copy an array in JavaScript with JSON.parse:
let orginalArray=
[
{firstName:"Choton", lastName:"Mohammad", age:26},
{firstName:"Mohammad", lastName:"Ishaque", age:26}
];
let copyArray = JSON.parse(JSON.stringify(orginalArray));
copyArray[0].age=27;
console.log("copyArray",copyArray);
console.log("orginalArray",orginalArray);

For this i use the new ECMAScript 6 Object.assign method :
let oldObject = [1,3,5,"test"];
let newObject = Object.assign({}, oldObject)
the first argument of this method is the array to be updated,
we pass an empty object because we want to have a completely new object,
also you can add other objects to be copied too :
let newObject = Object.assign({}, oldObject, o2, o3, ...)

Shifting the new variable also shifts the old original one

How come with this
var prodataTemp = [];
prodataTemp = prodata;
prodataTemp.shift();
both variable prodatTemp and prodata are shifted? I can see it in the console.

Assigning a JavaScript object to another variable, will not copy the contents, but it make the left hand side variable, a reference to the right hand side expression. So,
var prodataTemp = [];
made prodataTemp refer an empty array and then
prodataTemp = prodata;
makes prodataTemp refer the same array object prodata was pointing to. (So, the old empty array is no more referenced by prodataTemp).
To actually make a copy**, use Array.prototype.slice, like this
prodataTemp = prodata.slice();
Now, prodataTemp refers to the copy of the array prodata, so that shifting one will not affect the other.
** - The copy made is just a shallow copy. So, if you have an array of arrays, then a new array will be created with all the references to the elements of the old array. So, mutating one array element will have its impact in the other as well.

Javascript array index

Sorry for asking a noob question but if I have an array:
MyArray["2cd"]="blah1";
MyArray["3cx"]="blah3";
MyArray["8cz"]="blah2";
And a string myStr="2cd";
And then I use MyArray[myStr] to get the value of blah, how can I get the number I am accessing in the object/array or 0 in this case?

If I may read between the lines, it sounds like you're thinking that the code you posted:
MyArray["2cd"] = "blah1";
MyArray["3cx"] = "blah3";
MyArray["8cz"] = "blah2";
will automatically become the equivalent of:
MyArray[0] = MyArray["2cd"] = "blah1";
MyArray[1] = MyArray["3cx"] = "blah3";
MyArray[2] = MyArray["8cz"] = "blah2";
and therefore you can get the string "blah1" either of these two ways:
var foo = MyArray[0]; // sets foo to "blah1"
var bar = MyArray["2cd"] // also sets bar to "blah1"
But that's not how JavaScript works.
You certainly can set things up so you can use my MyArray[0] and MyArray["2cd"] to fetch the same value, but you have to do it explicitly as in my example.
One thing you didn't mention is how you declared MyArray itself. Is it an Array or an Object? That is, before the code you posted, did you create MyArray with:
var MyArray = {}; // or equivalently, var Array = new Object;
or:
var MyArray = []; // or equivalently, var Array = new Array;
The first example creates an Object, the second an Array.
What is a bit confusing is that JavaScript has both of these two types, which in many cases you can use somewhat interchangeably. But it's customary to use an Object when you are using arbitrary (generally but not necessarily non-numeric) keys into the object, as in your example. Conversely, it's customary to use an Array when you are primarily using strictly numeric indexes.
In fact, JavaScript's Array type inherits from the Object type. An Array is simply an Object with some additional behavior:
An Array has additional methods such as .push() which appends an item to the array.
An Array has a .length property which is automatically updated when you add elements with .push() or a direct array[123] assignment, or when you remove elements with .pop() or other methods.
What JavaScript doesn't have, as Fabrício pointed out, is an "associative array" that behaves like what you might find in some other languages. It has Objects and it has Arrays (which inherit from Objects), and you have to deal with each of those on their own terms.