Very simple example when I use function inside 'required' that should run on actual form validation but it also does execute on load of the page.

The question is how to avoid it and make so it would call other function inside required only on actual validation.

$("form").validate({           
            rules : {
                testinput: {
                    required: runFunction('hello world')
                }
});

function runFunction(a){
    console.log(a);
}

Very simple example when I use function inside 'required' that should run on actual form validation but it also does execute on load of the page.

The question is how to avoid it and make so it would call other function inside required only on actual validation.

$("form").validate({           
            rules : {
                testinput: {
                    required: runFunction('hello world')
                }
});

function runFunction(a){
    console.log(a);
}

• javascript
• jquery
• jquery-validate

3 Answers 3

You need to wrap your function call inside another function:

$("form").validate({           
    rules : {
        testinput: {
            required: function(el) {
                runFunction('hello world')
            }
        }
    });
});

The reason for this is because the value returned from runFunction is being set as the value of the required property on load. With the above code you are assigning a function to the required property which will only be run when validating.

Call function in required callback like,

$("form").validate({           
    rules : {
        testinput: {
             required: function(){ runFunction('hello world'); 
        }
    }
});

Read required-method

another way would be using some sort of partial application

see maybe: Partial Application - Eloquent Javascript

your code might then be something among this lines:

$("form").validate({           
    rules : {
        testinput: {
            required: partial(runFunction,'hello world')
        }
});

Where partial(runFunction,'hello world') creates a new function which is eqivalent to runFunction('hello world').

This a powerfull concept from functional programming, and JS can be extended to support such a thing.

EDIT: 1 might be a better explanation of partial application

http://www.drdobbs./open-source/currying-and-partial-functions-in-javasc/231001821