Knockout.js hasfocus

Question

I am updating data into database by entering value into the table cell, I need to set focus on the same cell if validation fails. this table is bounded through knockout.js view model.

self.FirstName = ko.observable(report.OverallRetention).extend({
  reportValueChange: {
    property: firstName
  }
});
ko.extenders.reportValueChange = function(target, option) {
    debugger;
    var _oldValue;
    target.setFocus = function(val) {
      target.hasfocus = val;
    };
    target.subscribe(function(oldValue) {
      _oldValue = oldValue;
    }, null, 'beforeChange');
    target.subscribe(function(newValue) { ///////Want to set set focus here.

Answer 1

wouldn't you just use the hasFocus data binding?

https://jsfiddle.net/0o89pmju/52/

click the clear name button and validation will fail. and the autofocus will be set on the first name.

I wasn't quite following your extender so I used the required one from the documentation http://knockoutjs.com/documentation/extenders.html

html

<p data-bind="css: { error: firstName.hasError }">
  <input data-bind='value: firstName, valueUpdate: "afterkeydown", hasFocus: firstName.hasError' />
  <span data-bind='visible: firstName.hasError, text: firstName.validationMessage'> </span>
</p>
<p data-bind="css: { error: lastName.hasError }">
  <input data-bind='value: lastName, valueUpdate: "afterkeydown"' />
  <span data-bind='visible: lastName.hasError, text: lastName.validationMessage'> </span>
</p>
<p>
  <button data-bind="click: clearName">clear first name</button>

  </button>
</p>

js

ko.extenders.required = function(target, overrideMessage) {
  //add some sub-observables to our observable
  target.hasError = ko.observable();
  target.validationMessage = ko.observable();

  //define a function to do validation
  function validate(newValue) {
    target.hasError(newValue ? false : true);
    target.validationMessage(newValue ? "" : overrideMessage || "This field is required");
  }

  //initial validation
  validate(target());

  //validate whenever the value changes
  target.subscribe(validate);

  //return the original observable
  return target;
};

function AppViewModel(first, last) {
  var self = this;
  this.firstName = ko.observable(first).extend({
    required: "Please enter a first name"
  });
  this.lastName = ko.observable(last).extend({
    required: ""
  });
  this.clearName = function() {
    self.firstName('');
    self.lastName('');
  }
}

ko.applyBindings(new AppViewModel("Bob", "Smith"));