Unable to download large data using javascript

Question

I have a large data in form of JSON object in the javascript. I have converted it into the string using JSON.stringify(). Now my use case is to provide this large string in a text file to the user. So for this i have written below code.

HTML code

  <button id='text_feed' type="submit">Generate ION Feed</button>

  <a href="data:attachment/txt" id="textLink" download="feed.txt"></a>

Javascript code

 var text = //huge string  

 $("#text_feed").click(function() {
        _generateFeed(text);
 });

 var _generateFeed = function(text) {
    //some code here
    $("#textLink").attr("href",
                          "data:attachment/txt," + encodeURIComponent(text))  [0].click();
    });
 }; 

Problem: When the string length is small , i am able to download the data . But when the string length goes higher (> 10^5) , my page crashes. This occurred because "encodeUriComponet(text)" is not able to encode large data.

I also tried window.open("data:attachment/txt," + encodeURIComponent(text)); But again my page got crashed because of the same reason that encodeURIComponet was unable to encode such a large string.

Another approach: I was also thinking of writing the data into a file using HTML5 File write API , but it has support only in Chrome web browser , but i need to make this work for atleast firefox and chrome both.

Use Case I don't want to do multiple downloads by breaking the data, as i need to have data in a single file in the end.

And my target is to support string of aprroximately 10^6 length. Can anyone help me how to download/write this amount of data into a single file.

Leonialeonid

How about URL.createObjectURL (new Blob(text, {type : 'text/plain'})); - does that work? – Lacylad

@RGraham Agreed, try the Blob API! – Faunie

Here’s a demo of that. Blob compiles a megabyte of text like it’s nothing. – Faunie

@RGraham and Xufox thanks. It works for me :) – Leonialeonid

Except don't forget to check the compatibility of URL and createObjectURL. – Belter

@user2509908 Don't worry, it's got better support than the [download] attribute itself :) @user3704217 you should leave an answer with the code to demonstrate how you solved it in the context of the problem! – Lacylad

@RGraham Fair enough. I didn't mean to undermine your answer. Just thought worth noting that many of these techniques are not as compatible as we think. You are correct, however. I can delete my comments if you wish :) – Belter

Not at all! That's not what I was getting at, just pointing out that if the [download] attribute it being used, that will most likely be the compatibility bottleneck :) Your comment is certainly valid! – Lacylad

I solved it as below. var _generateFeed = function(text) { /*some code here*/ var url = URL.createObjectURL( new Blob( [text], {type:'text/plain'} ) ); $("#textLink").attr("href",url)[0].click(); }; – Leonialeonid

wich one is your server? maybe a expressjs server?? It has a limit to json files.. – Furtado

@Leonialeonid This question should be closed if you found a solution. There's no need for it to appear on the unanswered list. – Haskel

"...must be released by calling URL.revokeObjectURL() when you no longer need them. Browsers will release these automatically when the document is unloaded; however, for optimal performance and memory usage, if there are safe times when you can explicitly unload them, you should do so." (from developer.mozilla.org/en-US/docs/Web/API/URL/createObjectURL ) – Empyreal

@Xufox, the demo do not work for me. Improve it by add download attribute to <a> element. See this demo – Tobi

Answer 1

From the OP:

I solved it as below.

var _generateFeed = function(text) {
    /*some code here*/
    var url = URL.createObjectURL( new Blob( [text], {type:'text/plain'} ) );
    $("#textLink").attr("href",url)[0].click();
}; 

Notes:

• URL.createObjectURL() is compatible with modern browsers and IE10+, but it is an unstable, experimental technology.
• Objects created using URL.createObjectURL() "must be released by calling URL.revokeObjectURL() when you no longer need them." - MDN

Murrey