为什么在函数中没有var保存这个变量，而不是全局的？
这个问题与I asked yesterday类似的javascript范围问题有关。我希望你能帮我解决这个问题。
我正在使用Chrome扩展程序。options.html将新的用户电子邮件保存为“用户”，并在background.html中调用refreshUser()函数。
//save entered gmail address
document.getElementById("save").addEventListener(
"click", function ()
{
var user = document.getElementById("getEmail").value;
localStorage.setItem("user", user);
chrome.extension.getBackgroundPage().refreshUser();
} , false)然后，我将电子邮件保存为"newUser“在background.html中。问题是newUser是在refreshUser()内部更新的，但它是refreshUser()之外的null
newUser = localStorage.getItem("user");
console.log("first newUser " + newUser);
//newUser=null
function refreshUser ()
{
newUser = localStorage.getItem("user");
console.log("newUser inside of refreshUser function " + newUser);
//newUser is updated with saved email in localStorage
}
console.log("newUser after refreshUser() " + newUser);
//newUser=null为什么在没有newUser关键字的情况下定义refreshUser()是本地的？谢谢你的帮忙!
更新
为了响应pimvdb's answer，我复制了background.html的代码。如果我想按指示在newUser中使用formData，需要在refreshUser()中调用哪个函数？谢谢。
<html>
<script>
newUser = localStorage.getItem("user");
console.log("first newUser " + newUser);
function refreshUser ()
{
newUser = localStorage.getItem("user");
console.log("newUser inside of refreshUser function " + newUser);
}
console.log("newUser after refreshUser() " + newUser);
//I want to user newUser below in formData
chrome.browserAction.onClicked.addListener(function(tab)
{
chrome.tabs.getSelected(null,
function(tab)
{
// Send a request to the content script.
chrome.tabs.sendRequest(tab.id, {action: "getDOM"},
function(response)
{
var firstParagraph = response.dom;
var formData = new FormData();
formData.append("url", tab.url);
formData.append("title", tab.title);
formData.append("pitch", firstParagraph);
formData.append("extension_user", "abc@gmail.com");
//I want to user newUser here:
//formData.append("extension_user", newUser);
console.log("newUser inside formData: " + newUser)
var xhr = new XMLHttpRequest();
xhr.open("POST", "http://ting-1.appspot.com/submithandlertest", true);
xhr.onreadystatechange =
function (aEvt)
{
if (xhr.readyState == 4)
{
if (xhr.status == 200)
{
console.log("request 200-OK");
chrome.browserAction.setBadgeText ( { text: "done" } );
setTimeout(function ()
{
chrome.browserAction.setBadgeText( { text: "" } );
}, 2000);
}
else
{
console.log("connection error");
chrome.browserAction.setBadgeText ( { text: "ERR" } );
}
}
};
xhr.send(formData);
}); //chrome.tabs.sendRequest
});
});
</script>
</html>响应的更新
我遇到的问题是，当浏览器打开时，background.html被加载，但是电子邮件随后保存在options.html中。所以refreshUser()告诉background.html从localStorage获取newUser。然后我需要在formData中使用“formData”，如下所示：
formData.append("extension_user", newUser);但是，我现在在refreshUser()之外使用“refreshUser()”的方式是空的。我遗漏了什么？
更新以澄清为什么某些日志没有显示在控制台中
我就是这样做的：
1. I reload the extension and start with localStorage empty
2. I use the extension to save a bookmark
3. all 3 logs are null as expected
first newUser null
newUser after refreshUser() null
newUser inside formData: null
request 200-ok
4. now I save user email in options as abc@gmail.com
5. now I use the extension again to save a bookmark
6. now refreshUser is executed and the log inside the function says abc@gmail.com and formData log says abc@gmail.com
newUser inside of refreshUser function abc@gmail.com
newUser inside formData: abc@gmail.com
request 200-OK
7. but what confuses me is that now the first 2 logs do not show in the console. Why?回答 3
Stack Overflow用户
发布于 2011-10-27 15:22:52
它是全球性的，但你在错误的时间访问它。
function refreshUser () { ... }只是一个函数声明；什么都没有真正执行。这两个声明之外的日志都会立即运行，此时尚未设置localStorage项(即是null)。
您的措辞"newUser after refreshUser()“相当矛盾。它确实是在声明之后执行的，但是newUser根本没有被更改，所以这两个日志都在函数日志null之外。您无法访问它时，它还没有设置，但你似乎期待。
由于全局变量已被更新，下面的日志应该是正确的。只需在refreshUser中设置它之后调用它。
function otherFunction() {
// logs the global variable 'newUser', which is thus indeed global
console.log("newUser inside otherFunction: " + newUser);
}
function refreshUser ()
{
newUser = localStorage.getItem("user");
otherFunction();
}Stack Overflow用户
发布于 2011-10-27 15:23:21
您还没有在发布的代码段中调用refreshUser()，所以不会设置它。
尝试调用它，然后检查全局newUser。
Stack Overflow用户
发布于 2011-10-27 15:37:15
我只想评论一下定义变量的做法，但这太长了，不能发表评论。
您永远不想定义没有var关键字的新变量，它会导致各种各样的欺骗和意外结果。如果要确保它是全局变量，请使用全局对象。
var globalObject = this,
globalVariable = 1; //or globalObject.globalVariable = 1;
function example(){
var globalVariable;
globalVariable = 2 //This will not set the global variable and you can see it's not intended either since we used var
console.log( globalObject.globalVariable );
globalObject.globalVariable = 2 // This will set the global variable, the intent to do so is very explicitly shown
console.log( globalObject.globalVariable );
}
example();
//1
//2
console.log( globalObject.globalVariable, globalVariable );
//2 2https://stackoverflow.com/questions/7918179
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