How to replace a given index element in knockoutjs

Question

How do you replace a given index in an observableArray with another element.

I have: ViewModel.Elements()[index]

how can i replace it with anot

Answer 1

Like dvijaz correctly points out, the accepted answer replaces a given value. This can cause problems when the given value is not unique in the array.

Instead of slicing the array and then gluing the array back together, I did the following which is more readable IMHO:

ViewModel.Elements()[index] = yourNewElement;
ViewModel.Elements.valueHasMutated();

Thanks to RP Niemeyer for pointing out how .replace works internally.

You can also extend observableArray to support this:

ko.observableArray.fn.replaceIndex = function(index, newValue) {
    this.valueWillMutate();
    this()[index] = newValue;
    this.valueHasMutated();
};

Which means you can do the following:

var arr = ko.observableArray([1, 2, 1, 4]);
arr.replaceIndex(2, 3); 
console.log(arr()); // logs [1, 2, 3, 4]