javascript - How to return from an async function - Stack Overflow

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My code looks like this:

myObject.myMethod('imageCheck', function () {
    var image = new Image();
    image.onerror = function() {
        return false;

    };  
    image.onload = function() {
        return true;
    };
    image.src = '.jpg';         
});

But, it doesn't work, assumedly because my returns only return from the anonymous function, not from the one called imageCheck. How can I rewrite this so that the whole function is returned as true or false?

My code looks like this:

myObject.myMethod('imageCheck', function () {
    var image = new Image();
    image.onerror = function() {
        return false;

    };  
    image.onload = function() {
        return true;
    };
    image.src = 'http://www.example./image.jpg';         
});

But, it doesn't work, assumedly because my returns only return from the anonymous function, not from the one called imageCheck. How can I rewrite this so that the whole function is returned as true or false?

• javascript
• asynchronous

Share Improve this question Follow asked Apr 27, 2011 at 19:13 Rich BradshawRich Bradshaw 73.1k4646 gold badges188188 silver badges241241 bronze badges 1

• What is myMethod and what is imageCheck? Why are you returning something in a handler function for an async call? That return data does not do anything. You have to use the "continuation" style of programming for async. – Stephen Chung Commented Apr 28, 2011 at 9:53

Add a ment  | 

1 Answer 1

Sorted by: Reset to default 6

you have to use callbacks, for example:

myObject.myMethod('imageCheck', function () {
    var image = new Image();
    image.onerror = function() {
        returnCallback(false);

    };  
    image.onload = function() {
        returnCallback(true);
    };
    image.src = 'http://www.example./image.jpg';         
});

function returnCallback(bool){
    //do something with bool
}

My code looks like this:

myObject.myMethod('imageCheck', function () {
    var image = new Image();
    image.onerror = function() {
        return false;

    };  
    image.onload = function() {
        return true;
    };
    image.src = '.jpg';         
});

But, it doesn't work, assumedly because my returns only return from the anonymous function, not from the one called imageCheck. How can I rewrite this so that the whole function is returned as true or false?

My code looks like this:

myObject.myMethod('imageCheck', function () {
    var image = new Image();
    image.onerror = function() {
        return false;

    };  
    image.onload = function() {
        return true;
    };
    image.src = 'http://www.example./image.jpg';         
});

But, it doesn't work, assumedly because my returns only return from the anonymous function, not from the one called imageCheck. How can I rewrite this so that the whole function is returned as true or false?

• javascript
• asynchronous

Share Improve this question Follow asked Apr 27, 2011 at 19:13 Rich BradshawRich Bradshaw 73.1k4646 gold badges188188 silver badges241241 bronze badges 1

• What is myMethod and what is imageCheck? Why are you returning something in a handler function for an async call? That return data does not do anything. You have to use the "continuation" style of programming for async. – Stephen Chung Commented Apr 28, 2011 at 9:53

Add a ment  | 

1 Answer 1

Sorted by: Reset to default 6

you have to use callbacks, for example:

myObject.myMethod('imageCheck', function () {
    var image = new Image();
    image.onerror = function() {
        returnCallback(false);

    };  
    image.onload = function() {
        returnCallback(true);
    };
    image.src = 'http://www.example./image.jpg';         
});

function returnCallback(bool){
    //do something with bool
}

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