[blockly] Document removal of nashorn support (#2428)
* remove nashorn Signed-off-by: Mark Herwege <mark.herwege@telenet.be> * fix image Signed-off-by: Mark Herwege <mark.herwege@telenet.be> * fix image position Signed-off-by: Mark Herwege <mark.herwege@telenet.be> --------- Signed-off-by: Mark Herwege <mark.herwege@telenet.be>pull/2432/head
Mark Herwege
GitHub
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@ -30,65 +30,28 @@ Also see this  [Intro](https
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## Blockly is a code generator or how the 🦏 found the holy Grail
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### Some history
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Even though you may not notice it directly, the blocks are eventually used to automatically create code that can run on the openHAB server.
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Please watch the  video [Blockly as an ECMA-Script code generator](https://youtu.be/EdllUlJ7p6k?t=1739) for a live demo.
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The code that is generated can be viewed when clicking the button  on the lower right corner of the blockly editor.
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In general, the code that Blockly generates is JavaScript (aka ECMAScript) which exists in several flavours or versions.
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The ECMAScript version that is used by Blockly in **openHAB 3** is **ECMAScript 5.1** and it is run by a component named **NashornJS** 🦏. [Nashorn JS](https://www.oracle.com/technical-resources/articles/java/jf14-nashorn.html) itself was part of Java until version 14 when it was dropped.
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The generated rule code is run within the Java runtime (also known as JVM) on the openHAB server and as openHAB 4 has moved to Java 17, the old ECMAScript 5.1 is not directly available anymore within the JVM via Nashorn.
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A replacement for the Nashorn JS is **GraalJS** ("the holy grail"), which is currently running **ECMAScript 2022** and therefore supports all modern JavaScript features, like arrow functions.
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[**GraalJS**](https://github.com/oracle/graaljs) is already available in openHAB 3 when the [JS Scripting Addon](https://www.openhab.org/addons/automation/jsscripting/) is installed.
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In general, the code that Blockly generates is JavaScript (aka ECMAScript).
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::: tip
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Please convert your old rules as quickly as possible because only with GraalJS you can leverage the openHAB JavaScript library (aka _openhab-js_) in Blockly.
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Using this library you can not only create much simpler code, it also allows **new functionality** that is not available with Nashorn.
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**Note that some blocks are only available with the openhab-js library on GraalJS.**
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Important: For Blockly to work, you need to have the [Javascript Scripting Addon](https://www.openhab.org/addons/automation/jsscripting/) (aka GraalJS) installed.
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:::
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### openHAB 3 / openHAB 4 - Migration
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### openHAB 3 / openHAB 4 to openHAB 4.3 or Later - Migration
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#### Migrating Blockly rules to openHAB 4 is easy
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From openHAB 4 onwards, the script engine is GraalJS provided by the [JS Scripting Addon](https://www.openhab.org/addons/automation/jsscripting/), **ECMAScript 2022**, when Blockly creates new scripts.
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OpenHAB versions before 4.3 could use **ECMAScript 2022** or **NashornJS** with **ECMAScript 5.1**, either installed by default or installed through an Addon.
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**NashornJS** is no longer an option with openHAB 4.3 or later. Therefore the generated Blockly code needs to be converted to **ECMAScript 2022**.
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From openHAB 4 on, the default script engine is GraalJS when Blockly creates new scripts.
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From a technical perspective a rule internally holds a so-called MIME-type that tells openHAB how the generated JavaScript language has to be interpreted.
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The (default) MIME-type `application/javascript` in openHAB 3 runs the rule with NashornJS, while this same MIME-type will run the Blocky rule with GraalJS in openHAB 4.
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As a result when running a non-converted openHAB 3 Blocky rule on openHAB 4, openHAB 4 will run a rule that was meant for NashornJS with GraalJS, which will fail.
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Therefore a conversion has to take place which in fact is not a lot of work:
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Converting is as easy as making sure the [JS Scripting Addon](https://www.openhab.org/addons/automation/jsscripting/) is installed, and opening your Blockly script.
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The UI will indicate your script has been generated with an older version and needs to be saved again.
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From that point onwards, things should work as before.
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There is the choice to
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- convert each rule to GraalJS
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- or keep the NashornJS Rules
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but both need some work on each blockly rule you have.
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#### Migration to GraalJS (recommended)
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- Make sure the [JS Scripting Addon](https://www.openhab.org/addons/automation/jsscripting/) addon is installed.
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- **To convert / migrate a rule that was created in openHAB 3 (NashornJS) to a GraalJS-compatible one for openHAB 4, simply open each Blockly rule once in openHAB 4 and save it - that's it.**
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- In this case, nothing more needs to be installed additionally to openHAB 4.
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#### Running openHAB 3 Blockly rules without migrating them right away
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- If you still want to run the Blockly rules that were created in openHAB 3 for the time being without changing them (see above), you have to install the [JavaScript Scripting (Nashorn) Addon](https://www.openhab.org/addons/automation/jsscriptingnashorn/) which provides backwards compatibility until you have converted all rules.
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- Open each Blockly rule or go to the Code TAB or Search for type: application/javascript;
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- Replace it by `application/javascript;version=ECMAScript-5.1`.
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Open the Blockly rule, find the following symbol and click on it.
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to choose the old version of JavaScript and then save the rule.
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- After the installation of the Addon both old rules created in openHAB 3 and new rules created in openHAB 4 can run on openHAB 4 at the same time.
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- After all scripts of the rules have been converted, like explained above, please uninstall the JavaScript Scripting (Nashorn) addon to save memory.
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- Note that this allows you to mix rules that run with NashornJS and some that run with GraalJS (see above).
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## Looking for help
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