Downloading a selected text on browser - browser extention

Question

I am trying to download a selected word or text on my browser (mozilla or chrome). When i select a word and right click on it, I can see the option "save this selected text to file" option. But I could not get the functionality working.It does not download the text. I am quite new to extention writing. I wanted to learn things by simple examples

manifest.json

    {
        "manifest_version":2,
        "version":"1.0",
        "name": "Selected Text Saver",
        "permissions": [
            "contextMenus",
            "activeTab"
        ],
        "background": {
        "scripts": ["main.js"]
        }
    }

main.js

    mouse1 = function(){
        chrome.tabs.executeScript({
            file: 'saver.js'
        });
    };

    chrome.contextMenus.create({
        title: "Save this selected text to file",
        contexts:["selection"],
        onclick: mouse1
    });

saver.js

    var text = window.getSelection().toString();
    var bb = new Blob([text], {type: 'text/plain'});
    var a = document.createElement('a');
    a.download = document.title.slice(0, 50).replace('/*[<>:/\\|?*]*/g', '') + '.txt';
    a.href = window.URL.createObjectURL(bb);
    a.dataset.downloadurl = ['text/plain', a.download, a.href].join(':');

Answer 1

The JavaScript at Question does not perform any further tasks with the created <a> element following a.dataset.downloadurl = ['text/plain', a.download, a.href].join(':');.

Append the created <a> element to document.body and call a.click() for user to be prompted offer for download of file.