Javascript reading files: how should I have asked?

[Trying2Learn]

TL;DR Summary

IO in javascript: what is the question

Hello

A few weeks ago (March 7) I asked how to have Javascript read a data file of numbers into an array.

I now understand why this is such a challenge when running a code on a web page, locally.

I have since found a sufficient workaround. I hope I can share it in the hope that someone can tell me how I SHOULD have asked the question. (Yes, this is an odd question: I am actually asking FOR a question.)

Here is what I did.

After Matlab processed all the numbers, I had Matlab open a file named "Rotation.js"
Matlab wrote the lines into Rotation.js to create an open of a function... then it deposited the data array.
Then it wrote the lines to "close the function."
Then it closed the file.

Then I ran the *.html file that ran the thereJS code. The main.js called the function that Matlab created, and displayed the
results in 3D.

So... I know that is a silly thing to have done (I KNOW I could have coded in OpenGL, or written the javascript code to process
the data. But considering the complexity of the Runge-Kutta method on six differential equations, this was a good workaround.

What SHOULD I have asked to have gotten this result? Again, i am not asking for an answer or even a better way. I just want to know how I could have asked the question.

Here is the section from Matlab to show you what I did.fileID = fopen('get_RotationMatrix.js','w');
fprintf(fileID,'function get_RotationMatrix(){\n');
fprintf(fileID,'var rotation = [\n');
for i = 1:timeIntegrationSteps
fprintf(fileID,'\"%12.8f\",\n',omega1(i));
end
fprintf(fileID,'];\n');
fprintf(fileID,'return rotation;\n}\n');
fclose(fileID);

 

[jedishrfu]

Nice workaround. In essence, you used a server-side program to create the necessary javascript containing your data that could then be retrieved by the browser and then processed on your web page.

In the context of javascript, your question is without meaning. I suppose if you had asked about processing data in Matlab and then how to display it on a web page you might gotten better responses but we'll never know as programming is such a diverse platform of recipes to do the same thing in different ways.

The problem with your question is that:
1) you are using javascript that traditionally works in a sandbox on a browser where local files simply can't be read or written.
2) you need to do things outside the browser to get it to work

NodeJS is a framework/server where you can use javascript on both the server-side and browser-side. In this case, javascript running on NodeJS can access files to read and to write.

You might read your binary data, compute stuff and then write out a JSON file with the data. There are methods that write data in JSON format for you.

The browser side of your application could request a computation and then retrieve the JSON file to process and display.

 

[pbuk]

What SHOULD I have asked to have gotten this result?

How about "I want to load a data file into an HTML page (so I can use it as input to the 3D renderer Three.js), how can I do this? I want all this to be local, not through a web server or anything."

 

[pbuk]

The browser side of your application could request a computation and then retrieve the JSON file to process and display.

That won't work with a local file, the XMLHttpRequest api won't work with file:// and although a script tag will happily parse a JSON file there is no way to access the data in the user sandbox.

 

[jedishrfu]

My apologies, that’s not what I meant the json data is sent back to the browser via the response to the request.