defs.js

Static scope analysis and transpilation of ES6 block scoped const and let variables, to ES3.

Node already supports const and let so you can use that today (run node --harmony and "use strict"). defs.js enables you to do the same for browser code. While developing you can rely on the experimental support in Chrome (chrome://flags, check Enable experimental JavaScript). defs.js is also a pretty decent static scope analyzer/linter.

Installation and usage

npm install -g defs

Then run it as defs file.js. The errors (if any) will go to stderr, the transpiled source to stdout, so redirect it like defs file.js > output.js. More command line options is coming.

Configuration

defs.js looks for a defs-config.json configuration file in your current directory. It will search for it in parent directories soon as you'd expect.

Example defs-config.json: javascript { "environments": ["node", "browser"],

"globals": {
    "my": false,
    "hat": true
},
"disallowVars": false,
"disallowDuplicated": true,
"disallowUnknownReferences": true

}

`globals` lets you list your program's globals, and indicate whether they are
writable (`true`) or read-only (`false`), just like `jshint`. `environments`
lets you import a set of pre-defined globals, here `node` and `browser`.
These default environments are borrowed from `jshint` (see
`jshint_globals/vars.js`).
* `disallowVars` (defaults to `false`) can be enabled to make
usage of `var` an error.
* `disallowDuplicated` (defaults to `true`) errors on duplicated
 `var` definitions in the same function scope.
* `disallowUnknownReferences` (defaults to `true`) errors on references to
 unknown global variables.


## Example

Input `example.js`:
```javascript
"use strict";
function fn() {
    const y = 0;
    for (let x = 0; x < 10; x++) {
        const y = x * 2;
        const z = y;
    }
    console.log(y); // prints 0
}
fn();

Output from ~ % defs example.js:

"use strict";
function fn() {
    var y = 0;
    for (var x = 0; x < 10; x++) {
        var y$0 = x * 2;
        var z = y$0;
    }
    console.log(y); // prints 0
}
fn();

License

MIT, see LICENSE file.