我如何使全局函数内定义的变量newUser？ [英] How can I make the variable newUser defined inside a function global?

问题描述

我将变量 newUser 从 options.html 发送到 background.html code> with chrome.extension.getBackgroundPage（）就像这样

  document.getElementById（save）。addEventListener（
click，function（）
 {
 var newUser = document.getElementById（getEmail）。value; 
 $ var bkg = chrome.extension.getBackgroundPage（）; 
 bkg.saveNewUser（newUser）; 
 console.log（newUser+ newUser）; 
}，false）
  

在 background.html 我有

 函数saveNewUser（newUser）
 {
 newUser = newUser; //这应该是全球性的？ 
 console.log（来自选项页面的新用户+ newUser）; 
} 
 
 console.log（newUser from options page+ newUser）; 
  

但是 newUser 是函数的局部。我的理解是，如果一个变量保存在没有关键字 var 的函数内，它应该是全局的。但在这种情况下并非如此。函数外的 console.log 会抛出未捕获的ReferenceError：newUser未定义错误。

我做错了什么，以及如何修改范围以在函数外部使用 newUser ？

谢谢。

编辑

background.html 但我仍然得到newUser undefined错误：

  var extension_user 
 
函数saveNewUser（newUser）
 {
 extension_user = newUser; // this should be global 
 console.log（extension_user from options page+ extension_user）; 
} 
 
 console.log（选项页面的extension_user+ extension_user）; 
  

更新

<我改变了两个页面来反映答案和评论，但仍然在函数之外，变量是未定义的。我做错了什么？

options.html

  document.getElementById（save）。addEventListener（
click，function（）
 {
 var newUserEmail = document.getElementById（getEmail）.value; 
 var bkg = chrome.extension.getBackgroundPage（）; 
 bkg.saveNewUser（newUserEmail）; 
 console.log（newUserEmail+ newUserEmail）; 
}，false）
  

background.html

  var newUser 
 
函数saveNewUser（newUserEmail）
 {
 window.newUser = newUserEmail; //这应该是全局的
 console.log（newUser from options page inside function+ newUser）; 
} 
 
 console.log（newUser from options page+ newUser）; 
  

解决方案

newUser saveNewUser 之前，c $ c>变量不存在于全局范围中。因此它给出了一个参考错误。只需在全局范围内将变量 newUser 声明为 var newUser; 。这应该可以解决问题。声明变量时，始终使用 var 关键字。这是一个很好的编程习惯。永远不要在本地范围内声明全局变量。你已经知道为什么。如果这个答案对您有帮助，请投票给我。 该代码澄清我的答案：

  var newUser; //新用户声明为全局
 
函数saveNewUser（newuser）
 {
 newUser = newuser; //这应该是全球性的？ 
 console.log（来自选项页面的新用户+ newUser）; 
} 
 
 console.log（newUser from options page+ newUser）; //没有更多的引用错误
  

I send the variable newUser from options.html to background.html with chrome.extension.getBackgroundPage() like this

document.getElementById("save").addEventListener(
    "click", function ()
    {
        var newUser = document.getElementById("getEmail").value;
        var bkg = chrome.extension.getBackgroundPage();
        bkg.saveNewUser(newUser);
        console.log("newUser " + newUser);
    } , false)

In background.html I have

function saveNewUser (newUser)
{
    newUser = newUser; //this should be global?
    console.log("newUser from options page " + newUser);
}

console.log("newUser from options page " + newUser);

but newUser is local to the function. My understanding is that if a variable is saved inside a function without the keyword var it should be global. But in this case it is not. The console.log outside the function throws Uncaught ReferenceError: newUser is not defined error.

What am I doing wrong and how can I fix the scope to use newUser outside the function?

Thanks.

Edit

I tried the following in background.html but I still get newUser undefined error:

var extension_user

function saveNewUser (newUser)
{
    extension_user = newUser; //this should be global
    console.log("extension_user from options page " + extension_user);
}

console.log("extension_user from options page " + extension_user);

Update

I changed both pages to reflect the answers and comments but still outside the function the variable is undefined. What am I doing wrong?

options.html

document.getElementById("save").addEventListener(
    "click", function ()
    {
        var newUserEmail = document.getElementById("getEmail").value;
        var bkg = chrome.extension.getBackgroundPage();
        bkg.saveNewUser(newUserEmail);
        console.log("newUserEmail " + newUserEmail);
    } , false)

background.html

var newUser

function saveNewUser (newUserEmail)
{
    window.newUser = newUserEmail; //this should be global
    console.log("newUser from options page inside function" + newUser);
}

console.log("newUser from options page " + newUser);

解决方案

The newUser variable does not exist in the global scope until the function saveNewUser is called. Thus it gives a reference error. Just declare the variable newUser in the global scope as var newUser;. That should solve the problem. Always use the var keyword when declaring variables. It's a good programming practice. Never declare global variables within local scopes. You already know why. Please vote for me if this answer helped you.

Edits:

Here's the code to clarify my answer:

var newUser; // new user declared as a global

function saveNewUser (newuser)
{
    newUser = newuser; // this should be global?
    console.log("newUser from options page " + newUser);
}

console.log("newUser from options page " + newUser); // no more reference error

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