I am using Greasemonkey/Tampermonkey to visit pages and make a change to a 100-element table based on what's on the current page.
Short term storage and array manipulation works fine, but I want to store the data permanently. I have tried GM_getValue/GM_setValue, GM_SuperValue, localStorage, and indexedDB, but I am clearly missing something fundamental.
Nothing seems to allow me to write the array into the permanent storage and then read it back into a variable where I can access each element, such that variablename[32] is actually the 32nd element in the table (Well, 33rd if you start counting at zero, which I do).
I need access to the entire 100-element table while the script is running, because I need to output some or all of it on the page itself. In the most basic case, I have a for loop which goes from 0 to 99, printing out the value of variablename[i] each time.
I have no predisposition to any method, I just want the frickin' thing to work in a Greasemonkey/Tampermonkey script.
Towards the top of the script I have this:
for (var i = 0; i <= 99; i++) {
currentData[i] = localStorage.getItem(currentData[i]);
}
The purpose of the above section is to read the 100 entries into the currentData array. That doesn't actually work for me now, probably because I'm not storing things properly in the first place.
In the middle, after modifying one of the elements, I want to replace it by doing this:
localStorage.setItem(
currentData[specificElementToChange], differentStuff);
The purpose of the above is to alter one of the 100 lines of data and store it permanently, so the next time the code at the top is read, it will pull out all 100 entries, with a single element changed by the above line.
That's the general principle.
I can't tell if what I'm doing isn't working because of some security issue with Firefox/Chrome or if what I want to do (permanently storing an array where each time I access a given page, one element changes) is impossible.
It's important that I access the array using the variable[element] format, but beyond that, any way I can store this data and retrieve it simply is fine with me.
I think you're going about this wrong. LocalStorage stores strings so the simplest way to store an array in LocalStorage is to stringify it into JSON and store the JSON. Then, when reading it back, you parse the JSON back into an array.
So, to read it in, you do this:
var currentData = JSON.parse(localStorage.getItem("currentData") || "[]");
To save your data, you do this:
localStorage.setItem("currentData", JSON.stringify(currentData));
Working demo: http://jsfiddle.net/jfriend00/6g5s6k1L/
When doing it this way, currentData is a variable that contains a normal array (after you've read in the data from LocalStorage). You can add items to it with .push(), read items with a numeric index such as:
var lastItem = currentData[currentData.length - 1];
Or, change an item in the array with:
currentData[0] = "newValue";
Of course, it's just a normal array, so you can use any array methods on it.
Related
I have certain requirements , I wanted to do the following in quickest way as possible.
I have 1000's of objects like below
{id:1,value:"value1"} . . {id:1000,value:"value1000"}
I want to access above objects by id
I want to clean the objects Lesser than certain id every few minutes (Because it generates 1000's of objects every second for my high frequency algorithm)
I can clean easily by using this.
myArray = myArray.filter(function( obj ) {
return obj.id > cleanSize;
});
I can find the object by id using
myArray.find(x => x.id === '45');
Problem is here , I feel that find is little slower when there is larger sets of data.So I created some objects of object like below
const id = 22;
myArray["x" + id] = {};
myArray["x" + id] = { id: id, value:"test" };
so I can access my item by id easily by myArray[x22]; , but problem is i am not able find the way to remove older items by id.
someone guide me better way to achieve the three points I mentioned above using arrays or objects.
The trouble with your question is, you're asking for a way to finish an algorithm that is supposed to solve a problem of yours, but I think there's something fundamentally wrong with the problem to begin with :)
If you store a sizeable amount of data records, each associated with an ID, and allow your code to access them freely, then you cannot have another part of your code dump some of them to the bin out of the blue (say, from within some timer callback) just because they are becoming "too old". You must be sure nobody is still working on them (and will ever need to) before deleting any of them.
If you don't explicitly synchronize the creation and deletion of your records, you might end up with a code that happens to work (because your objects happen to be processed quickly enough never to be deleted too early), but will be likely to break anytime (if your processing time increases and your data becomes "too old" before being fully processed).
This is especially true in the context of a browser. Your code is supposed to run on any computer connected to the Internet, which could have dozens of reasons to be running 10 or 100 times slower than the machine you test your code on. So making assumptions about the processing time of thousands of records is asking for serious trouble.
Without further specification, it seems to me answering your question would be like helping you finish a gun that would only allow you to shoot yourself in the foot :)
All this being said, any JavaScript object inherently does exactly what you ask for, provided you're okay with using strings for IDs, since an object property name can also be used as an index in an associative array.
var associative_array = {}
var bob = { id:1456, name:"Bob" }
var ted = { id:2375, name:"Ted" }
// store some data with arbitrary ids
associative_array[bob.id] = bob
associative_array[ted.id] = ted
console.log(JSON.stringify(associative_array)) // Bob and Ted
// access data by id
var some_guy = associative_array[2375] // index will be converted to string anyway
console.log(JSON.stringify(some_guy)) // Ted
var some_other_guy = associative_array["1456"]
console.log(JSON.stringify(some_other_guy)) // Bob
var some_AWOL_guy = associative_array[9999]
console.log(JSON.stringify(some_AWOL_guy)) // undefined
// delete data by id
delete associative_array[bob.id] // so long, Bob
console.log(JSON.stringify(associative_array)) // only Ted left
Though I doubt speed will really be an issue, this mechanism is about as fast as you will ever get JavaScript to run, since the underlying data structure is a hash table, theoretically O(1).
Anything involving array methods like find() or filter() will run in at least O(n).
Besides, each invocation of filter() would waste memory and CPU recreating the array to no avail.
I have a large set of embedded data fields that are called rnd1, rnd2, rnd3 etc. In a certain question block, I stored to each of these a certain value (each a different random number).
I also have a Loop and Merge question block, and in each round, I would like to access the stored data of a different field (i.e. in the 1st round I'd like to access whatever is in rnd1, in the 2nd round access rnd2 etc.) Can this be done in Qualtrics?
I tried something like:
Qualtrics.SurveyEngine.addOnload(function()
{
var trialNum = this.questionId.split('_')[0]; // getting the loop's current round number
var EDname = "rnd"+trialNum; // name of desired EF field
var rndNum = "${e://Field/" + EDname + "}"; // this is where I'd like stored the right ED value
// some more code that uses rndNum
});
but this does not work. It seems that while EDname gets the right string, I cannot access the value of that embedded field this way (though var rndNum = "${e://Field/rnd1} does work and returns the right value, so the problem seems to be in the looping strucutre).
If I cannot loop over the different fields in the JS code for some reason, is there another clever way to get that done in Qualtrics? For example, I thought it may be possible to use the different field names in the Loop and Merge section as "Field 2", but this seem to require me setting manually each and every ED field name.
Thanks.
Piped embedded data fields are resolved on the server before the page gets sent to your browser. So, it is impossible to dynamically create an embedded data field name and resolve it on the client side with JavaScript.
The way you are doing it with a loop & merge field is the best way.
I have the following hierarchy on firebase, some data are hidden for confidentiality:
I'm trying to get a list of videos IDs (underlines in red)
I only can get all nodes, then detect their names and store them in an array!
But this causes low performance; because the dataSnapshot from firebase is very big in my case, so I want to avoid retrieving all the nodes' content then loop over them to get IDs, I need to just retrieve the IDs only, i.e. without their nested elements.
Here's my code:
new Firebase("https://PRIVATE_NAME.firebaseio.com/videos/").once(
'value',
function(dataSnapshot){
// dataSnapshot now contains all the videos ids, lines & links
// this causes many performance issues
// Then I need to loop over all elements to extract ids !
var videoIdIndex = 0;
var videoIds = new Array();
dataSnapshot.forEach(
function(childSnapshot) {
videoIds[videoIdIndex++] = childSnapshot.name();
}
);
}
);
How may I retrieve only IDs to avoid lot of data transfer and to avoid looping over retrived data to get IDs ? is there a way to just retrive these IDs directly ?
UPDATE: There is now a shallow command in the REST API that will fetch just the keys for a path. This has not been added to the SDKs yet.
In Firebase, you can't obtain a list of node names without retrieving the data underneath. Not yet anyways. The performance problems can be addressed with normalization.
Essentially, your goal is to split data into consumable chunks. Store your list of video keys, possible with a couple meta fields like title, etc, in one path, and store the bulk content somewhere else. For example:
/video_meta/id/link, title, ...
/video_lines/id/...
To learn more about denormalizing, check out this article: https://www.firebase.com/blog/2013-04-12-denormalizing-is-normal.html
It is a bit old, and you probably already know, but in case someone else comes along. You can do this using REST api call, you only need to set the parameter shallow=true
here is the documentation
I'm currently making a Chrome Extension, and I'm at the last stage of it, storing the users preferences.
I know Local Storage will store strings, and at this stage I'm getting awway with just using strings, but as the storage requirements get bigger, a 2 dimentional array is required. I've seen that Local Storage is not capable of storaing an array, but you can use JSON. I've never used JSON, and when looking at examples, I do not understand how to do so.
for (i=1;i<=localStorage["totalwebsites"];i++) {
// Get the title of the current item
var title = localStorage["websitetitle" + i];
// Create the new context menu item, and get its menuItemId to store in the right localStorage string
var menuItemId = chrome.contextMenus.create({parentId: ParentID, title: title, contexts:["selection"], onclick: searchFromContext});
// Store the created menu items menuItemId in the array so we know which item was chosen later on
websitesarray[menuItemId] = localStorage["websiteurl" + i];
}
As you can see, this gets very messy, very quick, when using strings. I was hoping for totalwebsites to become a count of the items in the array, and websitetitle and websiteurl to be in the 2 dimetional array.
I don't see how you would do this in JSON, or at least how this could be permanently stored in Chrome itself. I'm guessing you'd have to convert it back to Local Storage Strings at some point or something? I don't think I'm getting this.
Any help/pointers would be much appreciated, I can't find much :(
Don't worry, JSON is super easy! Assuming that your websites are stored in websitesarray:
// To load:
websitesarray = JSON.parse(localstorage.websites);
// To store:
localstorage.websites = JSON.stringify(websitesarray);
Make sure you have a sane way to handle the case where localstorage.websites isn't set yet, as JSON.parse will throw a fit if its input is empty.
I am trying to make a page work for my website using the mootools framework. I have looked everywhere I can think of for answers as to why this isn't working, but have come up empty.
I want to populate several arrays with different data types from the html, and then, by calling elements from each array by index number, dynamically link and control those elements within functions. I was testing the simple snippet of code below in mootools jsfiddle utility. Trying to call an element from array "region" directly returns "undefined" and trying to return the index number of an element returns the null value of "-1".
I cannot get useful data out of this array. I can think of three possible reasons why, but cannot figure out how to identify what is really happening here:
1. Perhaps this array is not being populated with any data at all.
2. Perhaps it is being populated, but I am misunderstanding what sort of data is gotten by "document.getElementBytag()" and therefore, the data cannot be displayed with the "document.writeln()" statement. (Or am I forced to slavishly create all my arrays?)
3. Perhaps the problem is that an array created in this way is not indexed. (Or is there something I could do to index this array?)
html:
<div>Florida Virginia</div>
<div>California Nevada</div>
<div>Ohio Indiana</div>
<div>New York Massachussetts</div>
<div>Oregon Washington</div>
js:
var region = $$('div');
document.writeln(region[2]);
document.writeln(region.indexOf('Ohio Indiana'));
Thanks for helping a js newbie figure out what is going on in the guts of this array.
$$ will return a list of DOM elements. If you are only interested in the text of those DOM nodes, then extract that bit out first. As #Dimitar pointed out in the comments, calling get on an object of Elements will return an array possibly by iterating over each element in the collection and getting the property in question.
var region = $$('div').get('text');
console.log(region[2]); // Ohio Indiana
console.log(region.indexOf('Ohio Indiana')); // 2
Also use, console.log instead of document.writeln or document.write, reason being that calling this function will clear the entire document and replace it with whatever string was passed in.
See an example.