identifierfy

Rewrites an identifier string so it's valid according to ES2015. Works in
Node.js 6 and above.

Please see this awesome article by Mathias
Bynens for
background.

Installation

``
npm install identifierfy
`

Usage

The module has one default export, the identifierfy function:

`js
const identifierfy = require('identifierfy')
`

Call identifierfy() with an identifier string. It'll return a string that can
be used as an identifier, which is useful when writing Babel
plugins.

Characters that are not allowed in identifiers are dropped. Any character that
follows a removed character is uppercased, except if the dropped character was
at the front of the string.

If necessary the resulting identifier is prefixed with an underscore. This will
happen if the string is a reserved word or if the first character cannot be used
as the first character (but is fine as the second character).

This behavior can be overridden by passing a second options argument. This
should be an object. Set prefixReservedWords to false to avoid reserved
words being prefixed. Set prefixInvalidIdentifiers to false to avoid
prefixing identifiers where the first character cannot be used. These options
are useful if the resulting value is concatenated with other characters, making
it valid after all.

Note that null is returned if all characters from the original string are
dropped.

Examples

`js
identifierfy(input)
`

Input|Resulting identifier|Reason
:---|:---|:---
'class|'_class'|Reserved word
'42'|'_42'|Identifiers cannot start with a number
'-foo'|'foo'|The - is dropped, but since it's as the front f is not uppercased
'foo-bar🙊baz'|'fooBarBaz'|The - and 🙊 characters are dropped, and the following characters uppercased
'foo-9'|foo9|9 can't be uppercased of course 😉
'💩'|null|Sadly emojis cannot be used as identifiers 😢

`js
identifierfy(input, {prefixReservedWords: false})
`
Input|Resulting identifier|Reason
:---|:---|:---
'class|'class'|Reserved word, but prefixing is disabled
'42'|'_42'|Identifiers cannot start with a number

`js
identifierfy(input, {prefixInvalidIdentifiers: false})
`
Input|Resulting identifier|Reason
:---|:---|:---
'class|'_class'|Reserved word
'42'|'42'|Identifiers cannot start with a number, however prefixing is disabled so it's OK

`js
identifierfy(input, {prefixInvalidIdentifiers: false, prefixReservedWords: false})
`
Input|Resulting identifier|Reason
:---|:---|:---
'class|'class'|Reserved word, but prefixing is disabled
'42'|'42'`|Identifiers cannot start with a number, however prefixing is disabled so it's OK