js回调函数

3、因为函数在Javascript中是第一类对象，我们像对待对象一样对待函数，因此我们能像传递变量一样传递函数，在函数中返回函数，在其他函数中使用函数。当我们将一个回调函数作为参数传递给另一个函数是，我们仅仅传递了函数定义。我们并没有在参数中执行函数。我们并不传递像我们平时执行函数一样带有一对执行小括号()的函数。

4、需要注意的很重要的一点是回调函数并不会马上被执行。

3、setTimeout和setInterval方法

//注意到click方法中是一个函数而不是一个变量
//它就是回调函数

$("#btn_1").click(function() ...{
  alert("Btn 1 Clicked");
});    

					

var friends = ["Mike", "Stacy", "Andy", "Rick"];

friends.forEach(function (eachName, index)...{
console.log(index + 1 + ". " + eachName); // 1. Mike, 2. Stacy, 3. Andy, 4. Rick
});

			

function successCallback()...{
    //在发送之前做点什么
}     

function successCallback()...{
  //在信息被成功接收之后做点什么
}

function completeCallback()...{
  //在完成之后做点什么
}

function errorCallback()...{
    //当错误发生时做点什么
}

$.ajax(...{
    url:"http://fiddle.jshell.net/favicon.png",
    success:successCallback,
    complete:completeCallback,
    error:errorCallback

});

		

    function genericPoemMaker(name, gender) ...{
        console.log(name + " is finer than fine wine.");
        console.log("Altruistic and noble for the modern time.");
        console.log("Always admirably adorned with the latest style.");
        console.log("A " + gender + " of unfortunate tragedies who still manages a perpetual smile");
    }

        //callback，参数的最后一项，将会是我们在上面定义的genericPoemMaker函数
        function getUserInput(firstName, lastName, gender, callback) ...{
            var fullName = firstName + " " + lastName;

            // Make sure the callback is a function
            if (typeof callback === "function") ...{
            // Execute the callback function and pass the parameters to it
            callback(fullName, gender);
            }
        }    



    //调用getUserInput函数并将genericPoemMaker函数作为回调函数：   
    getUserInput("Michael", "Fassbender", "Man", genericPoemMaker);

    // 输出

			 Michael Fassbender is finer than fine wine.  Altruistic and noble for the modern time.  Always admirably adorned with the latest style.  A Man of unfortunate tragedies who still manages a perpetual smile.  

unction greetUser(customerName, sex)  ...{
   var salutation  = sex && sex === "Man" ? "Mr." : "Ms.";
  console.log("Hello, " + salutation + " " + customerName);
}

// 将greetUser作为一个回调函数
getUserInput("Bill", "Gates", "Man", greetUser);

// 这里是输出
Hello, Mr. Bill Gates