ES5 versions

[s100]

Recent changes in JSONata 1.2.x introduced the use of ES6 generators, but support for these is not universal, so an ES5-compatible version of JSONata is desirable.

• Added babel-cli as a development dependency in package.json.
• Added babel-preset-env as a development dependency in package.json - this provides a basic preset configuration for Babel, named "env".
• Added .babelrc to configure babel for this task. Note the use of the "env" preset, provided above.
• Added babel-runtime as a development dependency in package.json. This provides the transformation which turns ES6 generators into simple ES5 code.
• Added babel-plugin-transform-runtime as a development dependency in package.json. When ES6 code which makes use of generators is compiled to ES5, ordinarily the output ES5 code makes use of a global variable regeneratorRuntime to work... and just assumes that this global variable exists somehow. However, using this plugin means that the output ES5 code instead explicitly calls var _regenerator = require('babel-runtime/regenerator'); and uses _regenerator to accomplish the same result.
• Added the "transform-plugin" to .babelrc.
• Added a new NPM task, "babel", which uses the configuration supplied in .babelrc to compiles ./jsonata.js (ES6) to ./jsonata-es5.js (ES5).

Unfortunately this leaves us in a situation where jsonata-es5.js has an external dependency on babel-runtime/regenerator - previously, JSONata had no external dependencies, and we want to keep it that way. So a few more steps were needed:

• Added browserify as a development dependency in package.json.
• Added a new NPM task, "browserify", which takes jsonata-es5.js as input and browserifies it in place. Note the use of the --standalone jsonata flag, which makes it so that the jsonata module is exposed as a global variable in the resulting UMD module.
• Since browserify pulls in all needed modules, and jsonata currently makes use of Buffer, we find that browserify pulls in a full browser implemention of Buffer along with ieee754 and base64, which bloats the output. This is unnecessary, because Buffer is only used when jsonata is running on Node.js. Using global.Buffer instead of Buffer prevents this. (I wasn't able to find a browserify flag to accomplish this.)

And:

• Task "minify" minifies jsonata.js to jsonata.min.js. A new task "minify-es5" minifies jsonata-es5.js to jsonata-es5.min.js.
• jsonata-es5.js and jsonata-es5.min.js have been added to .eslintignore and .gitignore.

Possible future work:

• Separate out the JSONata source from its distribution, so that we can present jsonata.js as a properly bundled UMD module as well?
• Manually implement Base64 so that we don't have to rely on that unsightly Buffer hack and can bring JSONata back down to 0 external dependencies (at least in the ES6 case)?
• Is there a more elegant way to get that ES6 generator implementation in there, or replace it with something of our own?

[coveralls]

Coverage remained the same at 100.0% when pulling 7a4f8a7 on s100:master into b76b013 on jsonata-js:master.

[andrew-coleman]

nice job! - many thanks