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identifierfy

Rewrites an identifier string so its valid according to ES2015

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3yrs ago

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ISC

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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:

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

identifierfy(input)
InputResulting identifierReason
'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'foo99 can't be uppercased of course 😉
'💩'nullSadly emojis cannot be used as identifiers 😢
identifierfy(input, {prefixReservedWords: false})
InputResulting identifierReason
'class'class'Reserved word, but prefixing is disabled
'42''_42'Identifiers cannot start with a number
identifierfy(input, {prefixInvalidIdentifiers: false})
InputResulting identifierReason
'class'_class'Reserved word
'42''42'Identifiers cannot start with a number, however prefixing is disabled so it's OK
identifierfy(input, {prefixInvalidIdentifiers: false, prefixReservedWords: false})
InputResulting identifierReason
'class'class'Reserved word, but prefixing is disabled
'42''42'Identifiers cannot start with a number, however prefixing is disabled so it's OK

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