Tag: javascript

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React and Redux error: “_react.default.createContext is not a function”

I’m adding Redux to an existing React app, converting from Flux to Redux. After wrapping my root component with the <Provider> I got this error and the app doesn’t initialize:

_react.default.createContext is not a function

Doing a quick search found this post suggesting I’ve got a mismatch in versions between newest Redux versions and possibly older versions of React. This is possible as I’m updating an older React app I put together a couple of years ago. Quick way to test this, remove React and react-dom and add them back again.

Right now I have:

"react": "^15.4.1",
"react-dedux": "^0.4.0-beta.4",
"react-dom": "^15.4.1",
"react-redux": "^7.2.0"

Removed React and react-dom and added back latest versions:

"react": "^16.13.1",
"react-dedux": "^0.4.0-beta.4",
"react-dom": "^16.13.1",
"react-redux": "^7.2.0"

Restated my app, fixed!

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node.js, node-oracledb and Oracle Instant Client

To access an Oracle DB from an AWS Lambda function developed with node.js, you need to package you Lambda with shared libraries from Oracle’s Instant Client. The install instructions are here ( http://oracle.github.io/node-oracledb/INSTALL.html#quickstart ) but the only part that is really needed is the download location (since there’s no specific instructions for bundling the libs with an AWS Lambda): https://www.oracle.com/database/technologies/instant-client/linux-x86-64-downloads.html

Not all the Oracle Instant Client files are needed. From this older npm module to automate the packaging of the required libraries, I used this same list of required libraries:

libclntshcore.so.19.1
libclntsh.so.19.1
libmql1.so
libipc1.so
libnnz19.so
libons.so (not packaged in current Instant Client)
libociicus.so
libaio.so (from separate download - see next step)

libaio – if you’re on a Linux platform you can ‘apt-get install libaio’ or similar, but building my Lambda on a Mac I had to manually download the package and extract just the .so file from here (download the Arch Linux x64 package): https://pkgs.org/download/libaio

Put these in a /lib dir and zip up the folder and files. Use this to create a Lambda Layer.

For the Lambda itself install the node.js module for the api:

npm install –save node-oracledb

For examples in api usage, see the examples here: https://github.com/oracle/node-oracledb/tree/master/examples

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What happened to the proliferation of Java web frameworks from the early 2000s?

Back in the early 2000s if you were a Java developer working on building web apps, chances are you were using Apache Struts. It was the de facto, go-to web framework of it’s time, pretty much used everywhere by everyone (it was even noticeable online for it’s pattern of using ‘*.do’ URLs for its Actions). However, it wasn’t the only framework in town. Around early to mid 2000s there was an explosion of Java based web frameworks being developed, for a while it seems like it was the-thing-to-do to build your own web framework because after all, you know better than all the other guys right?

Joking aside, other major frameworks that appeared, some of the other big names were Wicket, Cocoon, Tapestry, Webwork (Webwork and Struts merged to form Struts 2), GWT and Vaadin. In the Java EE space the standard web framework became JSF but never really gained traction over any of the others. The one that stayed the course and probably the only one still in serious usage would be Spring Web MVC.

The funny thing about all this churn that occurred is that it feels like it’s all happening again, but now in the Javascript space. Sure, once we realized we could could offload some of this backend rendering of the UI to the frontend and after Google had shown the way with GMail showing us how the user experience of a single page app is far better than the traditional request/response of web apps we had become used to, it was inevitable that serverside based Java web frameworks would fall out of favor and get replaced by Javascript clientside frameworks. Was it inevitable that the industry would go through the same learning pains once again though? I’m not sure, but it happened.

At one point jQuery was the de facto JavaScript framework, much like Struts was in the Java space back in it’s time. Then came the flood: backbone, ember, Dojo, Knockout seemed to to be the main players, eventually settling down to ‘the big 3’ that we have today, Angular, React and Vue.

So what happened to all the Java web frameworks? Spring Web MVC is still around and still in use. With the change in technologies and a shift in focus from backend web frameworks to frontend, the backend web frameworks became less relevant. Could this shift happen again? Sure, when the next big things comes along.

Moral of the story: tech changes quick in software development. Keep an eye out for whats coming next, because what’s hot today can quickly become irrelevant tomorrow.

Additional reading: if you’re interested to read more about Java web frameworks, Zeroturnaround’s Rebel Labs used to do a survey on framework usage, and you can see their findings from their relatively recent reports, from 2014, 2015 and 2017:

https://www.jrebel.com/blog/java-tools-and-technologies-landscape-2014#Web%20Frameworks

https://www.jrebel.com/blog/java-web-framework-usage-stats

https://www.jrebel.com/blog/java-web-frameworks-index

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cal-heatmap with more than 6 heatmap ranges

By default cal-heatmap supports 5 ranges of values for the heatmap colors, so this config:

[10,20,30,40]

will give you the ranges:

  • 0 to 10
  • 11 to 20
  • 21 to 30
  • 31 to 40
  • > 40 (the 5th range)

If you attempt to define more than 5 ranges, cells in the 6th range and above will just have a default background color. In my www.spotviz.info app I tried to create 6 ranges, so the darkest color is for > 6000. On 9/28 and 9/29 (and the other blank dates in October in the screenshot below) have values more than 6000 but are showing as the default color:

The config I had for this was:

legend : [10,100,2000,4000,6000]

The ranges I was expecting from this config was:

  • 0 to 10
  • 11 to 100,
  • 101 to 2000
  • 2001 to 4000
  • 4001 to 6000
  • > 6000

Changing this to 4 values configuring 5 ranges fixed this issue:

legend : [1000, 2000, 4000, 6000]

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