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How to store a variable value obtained in home page across all pages?

I am using jquery to fetch inner html value of a div in home page, and I want this value to be accessible in all pages. The problem i'm facing is that the div from which i'm getting the value is present only in home page, so when the script runs in other page, the value will be undefined as the div is not present.
The issue is, they are displaying a message in bottom of home page and we want it to be displayed in top part of all pages. so I used jquery to extract the text content and display it in top part, but when we go to other pages, the script fails as the bottom of that page wont have the message.

store it in a local storage:
localStorage.setItem('myItem', myValue);
and then you could Access this item on all pages
var item = localStorage.getItem('myItem');
https://developer.mozilla.org/de/docs/Web/API/Window/localStorage

You can use web storage objects like: sessionStorage or localStorage,
but be careful with the data you store, which determines which method to use.
Data in sessionStorage is cleared when the page session ends.
Data stored in localStorage has no expiration time.

You can use Window localStorage Property as solution to your problem. Another option is sessionStorage. It depends what you trying to achieve. Look at the definition for both of them and use appropriate.

How to update or manipulate content loaded in iframe from parent?

I am trying to create some editor. What it does is I have several input fields in my current site, when user enter any word , I have seperate html rendered in iframe which is hosted separately which will have some title, subtitle and few other contents . so if user types in title input field. I want to update title in rendered html page located in iframe. please share what is the proper way to setup this scenario?
Tried to manipulate using DOM id, but its not very scalable and also laggy.
Currently checking websockets

I would assign every user an ID which is stored alongside their changes into a database. The iframe would display a php document which loads the values from the db and displays them as intended. On every change you simply reload the php with the corresponding id.

In this case, the answer is here yet: Loading a string if HTML into an iframe using JavaScript
You can do it with
document.getElementById('iframe').src =
"data:text/html;charset=utf-8," + escape(html);

Moving an HTML+javascript page to iFrame

I have an existing website composed of individual pages (each page is a different tool that requires some user input (ie forms), and each with it's own set of javascript functions to populate dropdown lists, etc on that page). Each of the tools is accessed from the main index.html.
Instead of each tool being its own "stand-alone" page that is invoked from index.html, I'd like each tool to be displayed in an iFrame instead on the main page. This way the main page remains static, while only updating the iframe with whatever tool the user selects. So say on the main index page, I have a 3 tools menu (collect logs, collect KPIs, collect status), along with an iFrame. If the user selects collect logs for example, the menu containing "collect logs" stays there, but the "collect logs" page is displayed in the iFrame.
My problem is that all the HTML content works fine, but none of the javascript code in the selected tool page works (ie none of the drop downs get populated since it's the javascript code in the page that does that by reading a file on the server).
Is there an easy way to port each tool page (html+javascript) to an iFrame without having to re-write tons of code (in my naivety I thought simply invoking the page inside an iFrame using target='' in the href would work)? Or is there a better method of accomplishing what I'm trying to do? Maybe iFrame isn't the solution.

Content in iframes remain autonomous from the wrapper app, so it makes sense that it's not working correctly. Other than building a listener for a click event associated with the div wrapped around the iframe, the iframe document isn't accessible if it points to a different origin. (See [same-origin policy]
(https://developer.mozilla.org/en-US/docs/Web/Security/Same-origin_policy))
To stay with simple html/css/js solution:
You can use a regular div to wrap each 'stand-alone' content and then just use whatever button/navigation target you have display that div and hide the previous by changing their css display style with the onClick event.
More invasive option:
You may want to consider using a more modular JS approach, like React JS, to build components vs pages and utilize React's structure to toggle components.
With react you can render each 'tool' when the user selects it . You would be able to utilize React component state as well to help in storing data and such for the life-cycle of the component.

Is it possible to make changes to a page source content variable through Ajax

Is it possible to make changes to the page source content through Ajax loaded by a jsp include in the main jsp ?
If not is it possible to reload that portion of the page alone (the jsp that loads some of the content) and to have a portion of the content in the page source changed ?
Details:
I've a variable called page this var gets its content from a java controller as a map of <String key,map<String key,String value>then it performs multiple actions and adds different params to the map, convert it to JSON and sends it to a jsp.
Recently I wanted to do something different,I want to add a param to the 'page' variable called contentOfThePage this variable gets its content dynamically when the document is fully loaded, after that I perform an Ajax request to the controller to add the new param, but the problem is that the new changes never makes it to the page source unless i reload the page or i navigate to another page and this is causing a lot of trouble as the page source may contain the page content of the previous page!
Any idea on how to avoid this and make changes to the page source (NOT DOM) directly ?
keep in mind that the contents are added dynamically but i need a way to change the page source without impacting the performance by requesting a reload after the ajax request succeeded

First You want to update some data that is already there after page load
you already have a json so a rest call i assume
you call it using ajax
now you added something else that you want to change
Yes it can be done actually
but not with the present set
i assume you have a single jsp and trying to change that jsp
well fit whatever you want to change in a panel like a graph or anything else
Add a button to top of the panel and on click the button url must be to the rest call so then data will be updated
I too have faced a similar problem with graphs,
i needed the graph to give updated data without refreshing the whole page,
so i put it inside a panel and wrote a rest controller that gives data for the graph and put a refresh button that calls this rest controller. This let me then update the graph without refreshing the rest of page

Safely reset (including running js) complete page to just like blank page

We provide live chat service to our customers. customer just copy some code and put in their footer. then they can have video chat, cobrowsing and many things..
but problem comes when user switch from page to page. so we have resume functionality as well. but thats not robost solution.
So i've come to two solution.
1. Iframe solution
i'll give client a some.html file which he'll need to upload to their root url, then upon video chat and cobrowse we load that page in some.html's iframe and chat appear in some.html
so that work well. chat box apprear seamlessly no page reload effects came in. and as its on same domain i can access all contents of iframe.
2. Another hack solution (not implemented yet, looks good solution)
i was thinking that instead of redirecting user to new page (some.html)
i should clear all contents of current page and load same url in one iframe within the page.
i think that will work well. but i affraid that some client might be using complex js based web app. so if i remove complete body from their page they might have problems.
as much as i know i can remove all dom nodes with their events handlers as well. but is their way to clean js runtime. so all js objects will destroyed and removed from scope so no longer run.
so is there a ways to clear any page completely with all its html and associated java-script as well. means reset page to blank.

Finally i found that there is no way to reset page.. but got another way to make it done.
upon need we can redirect user to same page with query string that identity that its reload for iframe, we put small bit of another code at head which remove all dom before loading dom, css, js.. and create just one iframe of same url.
thus it allows me, have user see no change in url, user browse website as normal without any problem and my chatbox always be there in same state across all pages.
will make it live soon on tagove.com

Why don't you empty the HTML page using empty() function of jquery first,
Then remove/update the link i.e.<script src="...."></script> so that the HTML has no dependency on that javascript and that way it won't be able to Modify the DOM.
And then try to build a javascript program to remove any file in the folder which is isolated(No calling, No dependency, no connection whatsoever)