Convert any string (even reserved words) to a valid javascript identifier.
Useful when writing compile to JS languages.
var toId = require('to-js-identifier');
//valid ids just go right through
toId('foo') === 'foo'
//convert your string to a valid js identifier
toId('not-js') === 'not$45$js'
//as use can see it wraps invalid chars with '$' + c.charCodeAt(0) + '$'
//Even though $ is a valid identifier, this function will escape it, so it
//is not possible that 2 inputs generate the same output
toId('$') === '$36$'
//reserved words are escaped
toId('null') === '$null$'
toId('var') === '$var$'
// yes I know undefined is technically an identifier, but it shouldn't be!!!
toId('undefined') === '$undefined$'MIT