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Home Interviews Passing data into components in Knockout – MindStick
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1 Answers

ICSM Computer
ICSM Computer 23 Apr 2025
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You can create components (kind of like reusable UI modules) and pass data into them using the params binding — similar to how you'd pass props in frameworks like Reactor Vue.

Let’s go step-by-step and learn how to create and use components with data-binding support. 

What Are Knockout Components?

  1. Reusable templates + ViewModels
  2. Encapsulate functionality
  3. Accept input via params

Basic Example: A hello-user component

Register the Component

ko.components.register('hello-user', {
  viewModel: function(params) {
    this.name = ko.observable(params.name); // passed from parent
  },
  template: `<div>Hello, <strong data-bind="text: name"></strong>!</div>`
});

Use It in HTML

<hello-user params="name: userName"></hello-user>

Parent ViewModel

function AppViewModel() {
  this.userName = ko.observable("Alice");
}

ko.applyBindings(new AppViewModel());

Now it’ll show: Hello, Alice!

params — How It Works

You can pass any data into the component:

  1. Primitive values
  2. Observables
  3. Objects
  4. Functions

Example:

<my-card params="title: 'Product', price: 99.99, inStock: true"></my-card>

Working with Multiple Params

ko.components.register('my-card', {
  viewModel: function(params) {
    this.title = params.title;
    this.price = params.price;
    this.inStock = params.inStock;
  },
  template: `
    <div>
      <h3 data-bind="text: title"></h3>
      <p>Price: $<span data-bind="text: price"></span></p>
      <span data-bind="visible: inStock">In stock</span>
      <span data-bind="visible: !inStock()">Out of stock</span>
    </div>
  `
});

Bonus: Passing Observable vs. Value

  1. If you pass an observable, the component will react to changes.
  2. If you pass a plain value, it's fixed at that time.

Example:

<hello-user params="name: userName"></hello-user>

If userName is observable and gets updated, the component will automatically reflect the change.

Summary

Feature Description
ko.components.register Defines the component
params Used to pass data from parent to component
template Inline or external HTML
Reactive props Use observables for dynamic updates
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