markdown-viewer/js/content.js

function injectCSS () {
    var link = document.createElement('link')
    link.rel = 'stylesheet'
    link.type = 'text/css'
    link.href = '#'
    link.id = 'theme'
    document.head.appendChild(link)
}

$(function () {
    injectCSS()
    
    $('body').addClass('markdown-body')//github
    $('pre').attr('id', 'markdown').hide()

    chrome.extension.sendMessage({
        message: 'markdown',
        markdown: $('#markdown').text()
    }, function (res) {
        $('body').append('<div id="html">').find('#html').append(res.marked)
        Prism.highlightAll()
    })

    chrome.extension.sendMessage({
        message: 'settings',
    }, function (data) {
        $('#theme').attr('href', chrome.extension.getURL('/themes/'+data.theme+'.css'))
        
        $('#theme').attr('disabled', data.raw)
        $('#markdown')[data.raw?'show':'hide']()
        $('#html')[data.raw?'hide':'show']()
    })

    $(window).on('load', function (e) {
        setTimeout(function () {
            var timeout = null
            $(window).on('scroll', function (e) {
                clearTimeout(timeout)
                timeout = setTimeout(function () {
                    localStorage.setItem('scrolltop', $(window).scrollTop())
                }, 100)
            })

            $(window).scrollTop(localStorage.getItem('scrolltop'))
        }, 100)
    })
})

chrome.extension.onMessage.addListener(function (req, sender, sendResponse) {
    switch (req.message) {
        case 'reload':
            window.location.reload(true)
            break
        
        case 'theme':
            var raw = $('#theme').attr('disabled') == 'disabled'
            $('#theme').remove()
            injectCSS()
            $('#theme').attr('href', chrome.extension.getURL('/themes/'+req.theme+'.css'))
            $('#theme').attr('disabled', raw)
            break

        case 'raw':
            $('#theme').attr('disabled', !($('#theme').attr('disabled') == 'disabled'))
            $('#markdown, #html').toggle()
            break
    }
})