knockout data-bind value. Need a string representation of an array, not a string with the array elements

Question

I need to set an 'input hidden' form element with an array generated from a knockout computed, to send it to the server within the form.

<input type="hidden" name="CourseSubjects" data-bind="value: allSelectedCourseSubjectsIds"/>

in my ViewModel:

self.allSelectedCourseSubjectsIds = ko.computed(function () {
        var result = [];
        for (var i = 0; i < self.CourseSubjects.length; i++) {                
            result = result.concat(self.CourseSubjects[i]().selectedCourseSubjects());
        }       

        return result;
    },self).extend({ rateLimit: { method: "notifyWhenChangesStop", timeout: 1000 } });

where self.CourseSubjects is an array of observable objects that contains a selectedCourseSubjects' observable array.

But the problem is that the hidden input's value is a string with a comma-separated list of Ids, while what i need is a string representation of the array. I mean, what i get as input hidden is:

<input type="hidden" name="CourseSubjects" value="1,2,3"/>

and what i need is

<input type="hidden" name="CourseSubjects" value="[1,2,3]"/>

Thank you.

Michael Best · Accepted Answer · 2017-10-11 19:47:22Z

1

The value of a binding can be a JavaScript expression.

data-bind="value: '[' + allSelectedCourseSubjectsIds() + ']'"/>

answered Oct 11, 2017 at 19:47

Michael Best

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Comments

Barry Franklin · Accepted Answer · 2017-10-11 19:25:16Z

0

How about overriding the toString method for Array?

Something like this:

Array.prototype.toString = function arrayToString() {
  var result = '';
  for (let i=0; i<this.length; i++){
     if (i !== this.length-1)
     { 
       result = result + this[i] + ', ';
     }
     else 
     {
        result = result + this[i];
     }
  }   
  return '[' + result + ']';
};

Note: this will make all Arrays appear this way when toString is called.

https://jsfiddle.net/aLot9aoc/30/

answered Oct 11, 2017 at 19:25

Barry Franklin

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1 Comment

Balázs Over a year ago

It is generally considered a bad practice to extend/override methods on built-in types. Mainly because you can never know whether other libraries used by your app rely on the default implementation.

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