javascript

Saving Console Messages in JavaScript

Have you ever encountered a situation where it would be beneficial to save whatever is written to the console across browser sessions?  If you have, you know there are not many solutions.  I recently decided that localStorage would be a good candidate to implement a solution to this problem with.

logsaver.js

logsaver.js is a lightweight, simple log preservation script.  It utilizes the flexibility of JavaScript to replace the default console.log function with a new, customized one.  Along with writing messages to the original console.log, this custom console.log  also writes messages to the specified localStorage key.

  • To start saving console.log messages, call startSavingLog().
  • To stop saving console.log messages, call stopSavingLog().
  • To clear saved console.log messages, call clearSavedLog().
  • To completely remove the localStorage key used by logsaver, call removeSavedLog().

For more information on options and how to use them, checkout the readme.

While you can copy the source below, I strongly recommend grabbing the latest from github here: logsaver.js.

Notes:

  • It doesn’t handle objects well.  Results in [Object object] appearing in the localStorage key value.  This is because localStorage is limited to strings.
  • It is possible to exceed the maximum space allocated to you in localStorage.  For desktop browsers, Chrome and Firefox have a 10 MB limit, while Safari and IE both have a 5 MB limit.  These number differs for mobile browsers.  More details.  In this event, logsaver.js will stop trying to save the log and display additional error messages in the console.

v0.1.0 Source

Posted by Chad Dotson in Doing Things Better, Misc, Programming, Software Engineering, Technology, Tips, 0 comments

Creating Web Workers From Functions (No File Needed)

So, you want to create a web worker from a function, the problem is all the examples examples show creating a web worker using a separate JavaScript file or from embedded JavaScript source.  There is a way to do it and that is using Blob URLs.  In the example below, I have taken the simple dedicated worker example from mdn and modified it appropriately.

First, we assume that we have a function that we want to serve as the source of the web worker.

Next, we use that function’s source to create the web worker.

See this example in action on jsfiddle here: http://jsfiddle.net/chaddotson/jr5p3L7r/

Notes:

  • The createObjectURL function is experimental according to MDN, so that is a bit of a warning bell.  However, according to caniuse, it is mostly safe across all browsers.
  • This can be used to create shared web workers, but they will not be shareable between tabs or windows.
  • This makes it more difficult, but possible to assemble dependencies for the web worker.
  • This isn’t the officially supported way to create a web worker.
  • I think this approach to creating a worker should be used sparingly, if ever.

 

Posted by Chad Dotson in Programming, Software Engineering, Tips, 0 comments

Creating Downloadable CSV (Or Any Other) Files In Browser With JavaScript

Many of us have wanted to create downloadable content straight from the browser.  I remember several years back where it was more difficult and the solutions were not clean.  Today, it is much much more simple and clean.  Enter Blob URLs.

In this example, I have an object of arrays.  These arrays may or may not all be the same length.  The csvify function accounts for this by letting the user optionally specify a default value and whether or not the pad at the beginning or at the end for arrays that aren’t the same size as the max.

It’s what comes after the csvify function that allows all this to work.  To make this csvified data downloadable, I first create a blob.  This blob contains the csv data and is created with the csv mime type.  I then create a url from that blob using createObjectURL and set that url as the href attribute on the download link.

Links:

Posted by Chad Dotson in Programming, Software Engineering, Technology, Tips, 0 comments

Notes On Writing Testable JavaScript Vol 1

When writing JavaScript, I am a big fan of minimizing functionality and variables exposed publicly, which we all know to be good practice. However, this leads to anonymous functions and functions hidden within closures.  So….

How Do You Test That?

How exactly do you test private methods in JavaScript?  To answer that you should ask yourself, should I even be testing them independently or can I write tests for the exposed functionality and still achieve code coverage?  If the answer to that question is “yes,” write tests for the exposed functionality that inherently test the underlying private functions and stop there.  If the answer is “no, I really need to test this function.”  There are a few approaches.

Member Variables For Testing Only

This approach involves creating member variables intended for testing and testing alone.  This method relies on the build process to remove the variables before going to production.  While this process works, I believe it has a code smell to it.  You are polluting and bloating the code base with needless variables.  If you are interested in the approach, here is an article about it.

The Real Question: Should It Be There?

Is the fact that you are asking this question an indicator of a code design issue?  Perhaps the code is in violation of the Single Responsibility Principle?  I’ve recently experienced a little epiphany associated with this.  I realized that a collection of private functions that I was hiding actually belonged to a separate object as public functions.  This refactoring drastically reduced the code complexity, made it more maintainable, and enabled small, important functions to be separately tested.

 

 

 

 

 

Posted by Chad Dotson in Programming, 1 comment

Generating JSON Documents From SQLite Databases In Python

Special Note

This article assumes that you do not wish to use a more sophisticated ORM tool such as SQLAlchemy.

Some Setup

Let’s start with a Q&D sqlite database given the following sql.

You can create the sqlite database given the following command.

Some Different Methods

For this example we want each record returned via the sql select statement to be its on JSON document.  There are several ways of doing this.  All of them solve the problem reasonably well but I was in search of the best way.  In checking python.org, I discovered that the sqlite connection object has an attribute falled row_factory.  This attribute can be modified provide selection results in a more advanced way.

Method 1 – My Preferred Method

From the python docs, we find that they already have a good factory for generating dictionaries.  It is my opinion that this functionality to should be more explicitly enabled in the language.

In this method, we override the row_factory attribute with a callable function that generates the python dictionary from the results.

 Method 2 – Almost As Good As Method 1

This method is just about as good as method 1.  Matter of fact, you can get away with this one and be just fine.  Functionally, the methods are almost identical.  With this method, the records can be accessed via index or via column name.  The biggest difference is that unlike method 1, these results don’t have the full functionality of a python dictionary.  For most people, this might be enough.

Putting It All Together

The following code snippet will extract a group of dictionaries based on the select statement from the sqlite database and dump it to JSON for display.

The Code

 The Results

 

 

Posted by Chad Dotson in Programming, Tips, 3 comments