如何从对象获取属性

Question

I'm using this code to retrieve a simple JSON object:

function userinfo() {
    var user = new Object();
    $.getJSON('###', function(data){
        user.id = data.user.uID;
        user.name = data.user.uname;
    });
    return user;
}
var user = userinfo();
console.log(user);

When I run console.log on the user object outside of the function, I can see the properties of the object (id, name). But when I try to console.log "user.id" or "user.name", they come up as undefined. I can't work out why this is, or what I can do to retrieve the properties without having to iterate over them.

Any suggestions?

Answer 1

The AJAX call to get the JSON is asynchronous, the callback function(data) isn't called until the AJAX returns, but you are reading user right after the AJAX request is sent, but before the AJAX response is received.

Try this:

function userinfo() {    
    $.getJSON('###', function(data){
        var user = new Object();
        user.id = data.user.uID;
        user.name = data.user.uname;
        // Do your stuff here
        console.log(user);
    });
}

userinfo();

Answer to comment: Just have a function like this on the app:

function processUser(user){
   console.log(user);
}

Then use it in the AJAX callback,

$.getJSON('###', function(data){
        var user = new Object();
        user.id = data.user.uID;
        user.name = data.user.uname;
        // Do your stuff here
        processUser(user);
    });

@Simon, you can do usual application logic in processUser() now, eg:

var usersList = []; // Assume this is a global for your app

function processUser(user){
   usersList.push(user);
   // now other parts of your app can find this user in the list
}

Answer 2

function userinfo(callback) {
    $.getJSON('###', function(data){
        callback({
            id: data.user.uId,
            name: data.user.uname
        });
    });
}
var user;
userinfo(function(newUser) {
    user = newUser;
    // do work with user.
});

// execution continues here before callback returns.  User will not be set.

user.name // error no property name of undefined.

Answer 3

Here's the fix:

function userinfo() {
    var user = new Object();
    $.ajax({
        async: false, //solution right here
        url: '/login/user.html',
        success: function (data) {
            user.id = data.user.uID;
            user.name = data.user.uname;
        }
    });
    return user;
}
var user = userinfo();
console.log(user.id);

Works perfectly.