Javascript 函数范围/执行顺序问题

Question

我对 javascript 范围/执行顺序有疑问。我在一个函数中创建了一个空对象。然后我在子函数中添加一些属性。但是，父函数中的属性没有改变。

$scope.finder = function (obj) {

    var id = obj.oid;

    var crit = MC.Criteria('_ownerUserOid == ?', [id]);

    theResult = {}; // Scope should be finder function.

    database.findOne(crit) // This is a Monaca method for finding from database

    .done(function(result) {
        // Returns and empty object as expected.
        console.log(JSON.stringify(theResult));

        theResult = result;

        // Returns the search result object as again expected.
        console.log(JSON.stringify(theResult));
    });



// Here's the issue - when I log and return theResult, I get an empty object again.
// I think it has to do something with the scope.
// Also, this logs to console before either of the console.logs in the done function.

    console.log(JSON.stringify(theResult));
    return theResult;


};

Answer 1

我想你在声明变量之前忘记了 "var"

var theResult = {}

Answer 2

您似乎正在对某些数据执行异步请求。任何时候执行异步 JavaScript，您都需要记住事情不是按顺序调用的。进行异步调用时，JavaScript 将继续执行堆栈下的代码。

在您的情况下，theResult 将是一个空对象，因为在您调用 console.log(JSON.stringify(theResult));

时 database.findOne(crit) 尚未完成执行

因此，您不能从 $scope.finder return，而是可以将回调传递给 $scope.finder 并在 database.findOne(crit) 完成执行后执行。

$scope.finder = function (obj, callback) {

    var id = obj.oid;

    var crit = MC.Criteria('_ownerUserOid == ?', [id]);

    theResult = {}; // Scope should be finder function.

    database.findOne(crit) // This is a Monaca method for finding from database

        .done(function(result) {
            // Returns and empty object as expected.
            console.log(JSON.stringify(theResult));

            theResult = result;

            callback(theResult);

            // Returns the search result object as again expected.
            console.log(JSON.stringify(theResult));
        });
};

那就这样称呼吧

$scope.finder({some: 'data'}, function(response) {
    // response now has the values of theResult
    console.log(response)
});

Answer 3

改成这样：

$scope.finder = function (obj) {   
    return database.findOne(MC.Criteria('_ownerUserOid == ?', [obj.oid]));        
};

// Client code:
finder({ oid: 'foo' })
  .then(function(result) { console.log(JSON.stringify(result)); });

Javascript 函数范围/执行顺序问题

Javascript function scope / order of execution issue

javascript

scope

monaca

order-of-execution