Chrome扩展程序 - 无法从上下文Manu打开弹出页面

Question

我正在学习Chrome扩展程序并尝试构建以下上下文菜单，该菜单应在选择文本时打开带有指向维基百科的链接的弹出窗口。这是我的代码

的manifest.json

{
    "manifest_version": 2,
    "name": "Wikit",
    "description": "Search Wikipedia on the go!",
    "version": "1.0",
    "icons" : {
        "16":"icon16.png",
        "48":"icon48.png",
        "128":"icon128.png"
    },
    "background": {
        "scripts": ["eventPage.js"],
        "persistent" : false
    },
    "permissions" : [
        "tabs",
        "contextMenus"
    ]
}

eventPage.js

var menuItem = {
    "id" : "wikit",
    "title" : "Wikit",
    "contexts" : [ "selection" ]
}
chrome.contextMenus.create(menuItem);

function fixedEncodeURI(str) {
    return encodeURI(str).replace(/%5B/g, '[').replace(/%5D/g, ']');
}

chrome.contextMenus.onClicked.addListener(function(clickData) {
    if (clickData.menuItemId == "wikit" && clickData.selectionText) {
        var wikiUrl = "https://en.wikipedia.org/wiki/"
                + fixedEncodeURI(clickData.selectionText);
        var createData = {
            "url" : wikiUrl,
            "type" : "popup",
            "top" : 5,
            "left" : 5,
            "width" : screen.availWidth / 2,
            "height" : screen.availHeight / 2
        };
        chrome.windows.create(createData, function() {
        });
    }
})

当我选择文本并单击Wikit时，它不会打开新的弹出/选项卡/页面。我做错了什么？