cookie.js

function setCookie( key , value , days){
    const d = new Date()
    d.setTime( d.getTime() + (days * 86400000 ))
    document.cookie = key + '=' + encodeURI( value ) + '; expires=' + d.toUTCString() + ';'
}
function getCookie( key ){
    if( document.cookie )
    {
        const pairs = decodeURI( document.cookie ).split(';')
        let i , name , value
        for(i = 0 ; i < pairs.length ; i++ )
        {
            name = ( pairs[ i ].split( '=' )[0]).trim()
            if( name === key ){ 
                value = pairs[ i ].split('=')[1]
            }

        }
        return value
    }
}
setCookie('User','Mike McGrath,12345', 7)

const list = document.getElementById( 'list' )
let i, value = getCookie( 'User' )
if( value.indexOf(','))
{
    value = value.split(',')
}
for( i = 0 ; i < value.length ; i++ )
{
    list.innerHTML += '<li>' + value[ i ]
}