njseries_02_03.js

class Router {
    ...

   _patternToRegex(pattern){
        let regex = ''
        let params = []
        let parts = pattern.split('/')
        for(let part of parts){
            if(part.trim() === '')
                continue
            if(part.startsWith(':')){
                if(part.endsWith('?')){
                    regex += '(/([_a-zA-Z0-9\\-]+))?' 
                } else {
                    regex += '/([_a-zA-Z0-9\\-]+)'
                }
                params.push(part.replace(/(\?|:)/g, ''))
                continue
            }
            regex += `/${part}`
        }
        // Handle special case (web root)
        if(regex === ''){
           regex = '/'  
        }
        regex = new RegExp(`^${regex}$`)
        return {regex , params}
    }

    ...
}