[英]how to access a variable from outside a function/instance
我有这个非常简单的JavaScript代码,应该使用参数firstname
和lastname
返回全名。当我在函数中提醒全名时,All都可以正常工作。 但是我正在努力如何使fullname
变量可以从函数/实例外部访问?
这是我的代码:
var getName = function () {
this.name = function (firstname, lastname, success) {
var fullName = firstname + " " + lastname;
success(fullName);
};
};
var test = new getName();
test.name("John", "Smith", function (output) {
var fullname = output;
alert(fullname); //this works fine
return fullname; // I need this variable to be accessed from outside this function
});
var myName = fullname; //I need to create the variable here
alert(myName); //this does not work
这是小提琴
非常感谢您的帮助。
编辑:我正在构建一个iPad应用程序,其中我使用了cordova和javascript插件。 其中一个插件使我可以访问设备内部的文件。 现在,我需要能够获取路径并在回调之外使用它,以便可以在范围内的任何地方使用:
这是插件代码:
var FileManager = function(){
this.get_path = function(todir,tofilename, success){
fail = (typeof fail == 'undefined')? Log('FileManager','read file fail'): fail;
this.load_file(
todir,
tofilename,
function(fileEntry){
var sPath = fileEntry.toURL();
success(sPath);
},
Log('fail')
);
}
this.load_file = function(dir, file, success, fail, dont_repeat){
if(!dir || dir =='')
{
Log('error','msg')('No file should be created, without a folder, to prevent a mess');
fail();
return;
}
fail = (typeof fail == 'undefined')? Log('FileManager','load file fail'): fail;
var full_file_path = dir+'/'+file;
var object = this;
// get fileSystem
fileSystemSingleton.load(
function(fs){
var dont_repeat_inner = dont_repeat;
// get file handler
console.log(fs.root);
fs.root.getFile(
full_file_path,
{create: true, exclusive: false},
success,
function(error){
if(dont_repeat == true){
Log('FileManager','error')('recurring error, gettingout of here!');
return;
}
// if target folder does not exist, create it
if(error.code == 3){
Log('FileManager','msg')('folder does not exist, creating it');
var a = new DirManager();
a.create_r(
dir,
function(){
Log('FileManager','mesg')('trying to create the file again: '+file);
object.load_file(dir,file,success,fail,true);
},
fail
);
return;
}
fail(error);
}
);
}
);
};
}
这是我的用法:
var b = new FileManager(); // Initialize a File manager
b.get_path('Documents','data.json',function(path){
myPath = path;
console.log(myPath); //this gives me the path of the file in the console, which works fine
return myPath; //I return the path to be accessed outside
});
var filePath = myPath; //here I need to access the path variable
console.log(filePath)// here, the path is undefined and it does not work
//Since I'm using angular services to retrieve the data from json, I'd like to pass the filePath
//this is a fraction of code for retrieving data:
return $resource('data.json',{}, {'query': {method: 'GET', isArray: false}});
//passing the value does not work
return $resource(filePath,{}, {'query': {method: 'GET', isArray: false}});
//even wrapping resource around instance does not work, it breaks the whole app
b.get_path('Documents','data.json',function(path){
myPath = path;
console.log(myPath); //this gives me the path of the file in the console, which works fine
return $resource(myPath,{}, {'query': {method: 'GET', isArray: false}});
});
工厂服务:
'use strict';
angular
.module ('myApp')
.factory('getMeData', function ($resource) {
var b = new FileManager(); // Initialize a File manager
b.get_path('Documents','data.json',function(path){
myPath = path;
return myPath;
});
//below doesn't work when passing path (it is undefined)
return $resource(myPath,{}, {'query': {method: 'GET', isArray: false}});
//when wrapping it around, the app crashes
b.get_path('Documents','data.json',function(path){
myPath = path;
return $resource(myPath,{}, {'query': {method: 'GET', isArray: false}});
});
//none of the solution above work
});
如果您具有name
函数,则返回success
的结果,那么您可以使用方法中的return。
即
var getName = function () {
this.name = function (firstname, lastname, success) {
var fullName = firstname + " " + lastname;
return success(fullName);
};
};
var test = new getName();
var myName = test.name("John", "Smith", function (output) {
var fullname = output;
alert(fullname); //this works fine
return fullname; // I need this variable to be accessed from outside this function
});
alert(myName);
在回调之外定义fullname
。
var getName = function () {
this.name = function (firstname, lastname, success) {
var fullName = firstname + " " + lastname;
success(fullName);
};
};
var test = new getName();
var fullname;
test.name("John", "Smith", function (output) {
fullname = output;
alert(fullname); //this works fine
return fullname; // I need this variable to be accessed from outside this function
});
alert(fullname);
希望能帮助到你。 小提琴
如果需要异步:
假设实际的代码源是一个异步代码,现在已从您的注释中确认,您应该只在回调中处理结果。 该值在回调之外根本不可用,因为结果稍后到达。
@Jim和@ bestmike007的答案不适用于异步操作,因为它从回调内部返回一个值,该回调可能在函数运行很长时间后发生。 (注意:@ bestmike007确实在注释中链接了一个改进的答案)。
例如,看看这里发生了什么: http : //fiddle.jshell.net/y1m36w9p/1/或这里http://jsfiddle.net/TrueBlueAussie/opczeuqw/1/
使用异步代码的唯一方法是异步方式。 这意味着您只能在回调内部处理结果:
// Get the fullname asyc and process the result
test.name("John", "Smith", function (fullname) {
alert(fullname); // you can only work with the result in here
});
另一种方法是返回一个jQuery promise
从getName.name()
但最终的结果仍然是回调做的工作,但是这一次它是这样的:
test.name("John", "Smith").done(function(fullname){
alert(fullname); // you can only work with the result in here
});
但这是更多的代码和复杂性,暂时没有额外的好处。
对于您特定的更新示例代码:
我对Angular不够熟悉,无法确认这一点,因此需要了解如何getMeData
,但是您应该使用另一个回调作为注册的getMeData
函数的参数:
'use strict';
angular
.module ('myApp')
.factory('getMeData', function ($resource, callback) {
var b = new FileManager(); // Initialize a File manager
b.get_path('Documents','data.json',function(path){
callback($resource(path,{}, {'query': {method: 'GET', isArray: false}}));
});
});
如果异步不需要 (废弃的选项)
如果(如下面先前的矛盾评论所述)这并不意味着要异步,那么根本不要使用回调,只需返回值的简单函数/方法即可: http : //fiddle.jshell.net/y1m36w9p/2/
例如
var getName = function () {
this.name = function (firstname, lastname) {
return firstname + " " + lastname;
};
};
// Create a instance of the getName class
var test = new getName();
// Get the fullname asyc and process the result
var fullname = test.name("John", "Smith");
// Do what you like with the value returned from the function
alert(fullname);
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