调用函数时出现未捕获的SyntaxError：意外令牌）

Question

I am wanting to write some code to return some data from an aJax call.

Here is the resource that I am referring to: http://www.w3schools.com/jquery/ajax_ajax.asp

Here is the code that I have written:

var data = getData("http://www.file.txt", function(result));
alert(data);

function getData(dataUrl, result)
{
    $.ajax({url: dataUrl, success: function(result){
        return result;
    }});
}

I am getting the following error:

Uncaught SyntaxError: Unexpected token )

At this line of code:

var data = getData("http://www.file.txt", function(result));

Also, is the above code efficient when getting large amounts of data?

Thanks

Answer 1

This is not the correct syntax for a callback, plus the asynchronous call doesn't quite work like that. Try this instead - data is set in the callback.

var data;
getData("http://www.file.txt"); 

function getData(dataUrl)
{
    $.ajax({url: dataUrl, success: function(result){
        data = result;
        alert(data);            
    }});
}

Answer 2

From JavaScript basics, a function should satisfy following.

1. A JavaScript function is defined with the function keyword, followed by a name, followed by parentheses ().
2. A function is basically a JavaScript object. So, The parentheses are required,as they set apart a function from the other items of your script or web page.

So the line of code is actually incorrect.

var data = getData("http://www.file.txt", function(result));

It should be either of the below.

var data = getData("http://www.file.txt", function(result) {
    //anonymous function body
});

or

var data = getData("http://www.file.txt", callbackFn(result));

function callbackFn(result) {
    //function body goes here.
}

Answer 3

You are not passing brackets so you get Uncaught SyntaxError: Unexpected token) error

 var data = getData("http://www.file.txt", function(result){}); 

But I think you have to use function like this

 function getData() { return Promise(function(resolve, reject) { $.ajax({ // ... success: function(data) { resolve(data); }, error: function(jqxhr, status, error) { reject(error); } }); }); } getData("http://www.file.txt").then(function(result) { console.log(result); }).catch(function() { // an error occurred }); 

Answer 4

If you are using ajax call, then you must use success or .then with it to be executed as callback after receiving data.

The code should be only this:

var data = '';
$.ajax({url: dataUrl, success: function(result){
        data = result;
        alert(data);
    }});