Contributing

This document contains rules and guidelines for porting the library from Java to TypeScript.

Tooling

Local development using Node.js and npm or yarn, see package.json for dependencies.

Note: Keep dependencies at minimum necessary. 🖤

Run the docs

To run the docs, open the CLI in this project root folder (something like <somepath>/zxing-js/library):

user@computer BUILDV <somepath>/zxing-js/library (develop)
http-server ./docs -a localhost -p 4040 -o

Note: http-server is a package that runs a local server, install with npm i -g http-server.

Porting

Initial port from 3.3.1-SNAPSHOT on May 2017 by Adrian Toșcă (@aleris).

Approach

The Java files are transformed using regexps for some obvious syntax transformation (see ./autotransform) and then modified manually.

Using http://www.jsweet.org was considered but rejected because of loosing type information early on (for example number versus int is essential for bitwise operations), language style and older TypeScript version.

Rules

• Keep all types as close to the original as possible.
• Keep detailed type information in comments where applicable (example int will become number /*int*/) as the code is extensively using bitwise operations that can overflow.
• Use TypedArray whenever possible (example int[] will become Int32Array) - see below for more info.
• Use constructor property whenever possible.
• Take care of array initialisation with capacity, especially when using length and push later on. Basically only use when setting with index accessor only .
• Use utility classes to implement platform dependencies (like System or Arrays), avoid inline implementation for anything that is not trivial.
• Use single class|enum|interface per module, export with default. Move internal classes to separate modules if used from other modules.
• Package level visibility will transform to public to avoid module complexity.
• Keep enum as similar with the original interface as possible (transform to class and use static fields for enum values).
• Always use === for == to avoid glitches from type transforms.

Cheat Sheet 💩

Java	TypeScript
byte[]	Uint8ClampedArray
int[]	Int32Array

Types

Java types

https://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html

• byte has 8 bits, signed (e.g. -127 to 127), so byte[] would transforms to Int8Array however:
  • TextEncoder will use Uint8Array.
  • canvas image data will use Uint8ClampedArray.
• int has 32 bits, signed, so int[] transforms to Int32Array.
• char has 2 bytes, so char[] transforms to Uint16Array.
• long has 64 bit two's complement integer, can be signed or unsigned.

JavaScript's TypedArray

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray

Things to look for

• Take care of int -> number (integer to number) port when doing bitwise transformation especially <<. Do a & 0xFFFFFFFF for ints, a &0xFF for bytes.
• Take care of array initialization, in Java new Array(N) initializes capacity NOT size/length.
• Use Math.floor for any division of ints otherwise the number type is a floating point and keeps the numbers after the dot.
• For float to int casting use Math.trunc, to replicate the same effect as Java casting does.

Encoding

In Java new String(<ByteArray>, encoding), a lot of encodings are supported See StringEncoding.ts for implementation in TypeScript for handling limited browser support. Will became: StringEncoding.decode(<ByteArray>, encoding).

TODO

• Check for sometype[] arrays: check for push, check for == length etc. To spot size comparison bugs.
• Skipped:
  • BufferedImageLuminanceSource.java
  • common/AbstractNegativeBlackBoxTestCase.java
  • common/AbstractBlackBoxTestCase.java
• Cp437 not supported by TextEncoding library see DecodedBitStreamParserTestCase.
• Replace instanceof with something more robust.
• Simplify double null !== <something> && undefined !== <something> checks.

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Most of things here are opinions and were written by the first porter, please feel free to discuss and help us to make it better.