unreachable-branch-transform

unreachable-branch-transform
============================


Removes unreachable code branches in if statements, ternaries ?, and logical operations || &&, where the test is determinable (like comparing two constants). This is similar to what UglifyJS's "dead_code" compressor option does, but without the extra code transformations.

When combined with something like envify and browserify, you can perform conditional require calls without including more code than you need.

#### Install ####

``bash
npm install unreachable-branch-transform
`

#### Example outputs #####

`js
// original
var transport = process.env.TARGET === 'client' ? require('ajax') : require('fs');

// after envify
var transport = 'server' === 'client' ? require('ajax') : require('fs');
// then after unreachable-branch-transform
var transport = require('fs');
`

`js
// original
if (process.env.NODE_ENV === 'development') {
console.log('in dev mode');
} else {
console.log('in some other mode');
}

// after envify
if ('production' === 'development') {
console.log('in dev mode');
} else {
console.log('in some other mode');
}

// then after unreachable-branch-transform
{
console.log('in some other mode');
}
`

#### Usage

* unreachable-branch-transform can be used a browserify transform. Just include it like any other transform.
* unreachable-branch-transform can also be used on raw code by calling the transform function exposed by requiring the package.

#### Frequently asked questions ####

##### Why are undefined equality references not removed?

If you have a branch with the format

`javascript
if (undefined === 'production') {
/ ... /
}
`

it will not be removed. Unfortunately, undefined is _not_ a constant in older browser runtimes and can be reassigned. In this case, it could be possible that undefined does indeed equal 'production'.

Credit
------
esmangle-evaluator` is from the esmangle project.