updating "placeholder" attribute using knockout

Question

I have a form with some fields getting some data using knockout.js (ver. 2.1.0). For example, to update the "value" field of an input I put:

<input type="text"  name="contrasena" id="login-user" value="" placeholder="" data-bind="value: user">

I have a JSON to store the value a I want to use for "pass" keyword, and it works correctly.

I tried to set "placeholder" attribute using the same method, but it doesn't works:

<input type="text"  name="contrasena" id="login-user" placeholder="" data-bind="placeholder: user">

I tried to modify knockout.js file adding "ko.bindingHandlers['placeholder']" function based on "ko.bindingHandlers['value']" (modifying "placeholder" instead of "value" in "ko.jsonExpressionRewriting.writeValueToProperty" function), but it doesn't work correctly, it puts the information in "value" attribute instead of "placeholder".

Anyone knows the way to solve this?

Thank you very much!

Answer 1

You should use the existing attr binding, like this:

<input data-bind="attr: {placeholder: ph}" />

var Model = function () {
    this.ph = ko.observable("Text..."); 
}
ko.applyBindings(new Model());