Knockoutjs computed passing parameters

Question

I am wondering if it is possible with knockoutjs to pass arguments when binding.

I am binding a list of checkboxes and would like to bind to a single computed observabl

Answer 1

There is no reason to use a computed value. Simply define a function in your View Model and bind the checked to it.

Below is a very simplistic example.

--

HTML

​

JS

var MyViewModel=function(){
    this.isEven = function(num) {
        return (num % 2) == 0;
    };
};
ko.applyBindings(new MyViewModel());

​--

That being said it is a good idea to try and push as much of the logic into your View Model as is possible. It would be advisable to create a View Model that models your checkbox as an object, and then the logic as to if the checkbox should be checked could be encapsulated inside.

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EDIT: Based on the requirement to do two-way binding I have written an extender to manage an observable.

http://jsfiddle.net/jearles/j6zLW/5/

ko.extenders.bitwise = function(target, bitCount) { 
    target.bits = [];    
    target.checked = ko.observableArray();

    // Create bit array based on requested number of bits
    for (i=bitCount-1; i>=0; i--) {
        target.bits.push(''+Math.pow(2, i));
    }        

    // Define a function to create bits
    function makeBits(newValue) {
       var num = !isNaN(newValue) ? parseInt(newValue) : 0;
       var arr = [];
       for (i=0; i -1) num += parseInt(target.bits[i]);
       }
       target(num);
    }

    // Create initial bits
    makeBits(target());

    // Make bits whenever the value changes
    target.subscribe(makeBits);

    // Make number whenever the bits change
    target.checked.subscribe(makeBitwise);

    // Return the original observable
    return target;
};

var MyViewModel=function(){
    var self = this;
    this.number = ko.observable(2).extend({ bitwise: 8});

};
ko.applyBindings(new MyViewModel());​