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Revati S Misra

Revati S Misra

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Ashutosh Kumar Verma

Ashutosh Kumar Verma

27-Jun-2024

Complex Databinding binding

Handling complex data binding scenarios in Knockout.js takes full advantage of its powerful features. Here is a structured approach to these types of issues.

ViewModel Settings

Arrange your visual models logically by being able to nest visual models with each other when they are needed to represent complex data relationships.
Use observables (ko.observable()), observables arrays (ko.observableArray()), and computed observables (ko.computed()) as needed to monitor and handle state variables.

Data Binding
Use the data-bind attribute on your HTML elements to bind them to the properties and functions of your view model.
Change binding types like text, value, visible, foreach, etc. depending on your UI needs.

Computed Observations
Use computed observables to derive values ​​or perform complex calculations based on other observables in your view model.
Computed searches update themselves whenever users change, ensuring that your UI stays consistent with your data.

Custom Bindings
Create custom bindings using ko.bindingHandlers to maintain complex UI behavior that is not covered by built-in bindings.
Report packaging helps maintain clean and reusable code with complex interfaces or visual elements.

Event Handling

Use event bindings to handle user interactions like clicks and key presses, and update your visual model accordingly.
Avoid manipulating the DOM directly; Instead, let Knockout.js handle data flow and UI updates.
Templates

Use templates (ko.template or ko.templateBinding) to define a reusable HTML structure that is bound to specific parts of your visual model.
Templates are particularly useful for defining aggregated data (e.g., lists of objects) or complex UI components.

Example- 

here is a simple example for the Task Management that demonstrates the data bindings in knockout.js,

Index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <link href="https://cdn.jsdelivr.net/npm/bootstrap@5.3.3/dist/css/bootstrap.min.css" rel="stylesheet" >
    <script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.5.1/knockout-latest.js"></script>
        <title>To do List Example</title>
</head>
<body>
    <div class="container">
        <div class="row">
            <div class="col-12">
                <h2>Task Manager</h2>    
                <div>
                    <input type="text" data-bind="value: newTaskTitle, event: { keyup: addTask }" class="form-control" placeholder="Add new task">
                    <button data-bind="click: addTask" class="btn btn-primary my-2">Add Task</button>
                </div>
                <div>
                    <table  class="table">
                        <thead>
                            <tr>
                                <th>#</th>                                
                                <th>Title</th>
                                <th>Date</th>
                                <th>Action</th>
                            </tr>
                        </thead>
                        <tbody data-bind="foreach: tasks">
                            <tr>
                                <td data-bind="text: $index() + 1"></td>
                                <td data-bind="text: title"></td>
                                <td data-bind="text: dueDate"></td>
                                <td>                                  
                                    <button data-bind="click: $parent.removeTask" class="btn btn-sm btn-outline-danger">Remove</button>
                                </td>
                            </tr>
                        </tbody>
                    </table>
                </div>            
            </div>
        </div>
    </div>
    <script src="app.js"></script>
</body>
</html>

 

app.js file

// Define TaskViewModel
function TaskViewModel() {
    var self = this;

    // Observable array to hold tasks
    self.tasks = ko.observableArray([
        {title: 'This is first task', dueDate: new Date().toLocaleDateString() },
        {title: 'This is second task', dueDate: new Date().toLocaleDateString() }
    ]);

    // Observable for new task title input
    self.newTaskTitle = ko.observable('');

    // Function to add a new task
    self.addTask = function(data, event) {
        if (event.type === 'click' || event.keyCode === 13) { // Enter key
            var newTitle = self.newTaskTitle().trim();
            if (newTitle) {
                self.tasks.push({
                    title: newTitle,
                    dueDate: new Date().toLocaleDateString()
                });
                self.newTaskTitle('');
            }
        }
    };

    // Function to remove a task
    self.removeTask = function(task) {
        self.tasks.remove(task);
    };    
}

// Apply bindings
ko.applyBindings(new TaskViewModel());

In the above example-
TaskViewModel: Defines the view model using Knockout.js.

  • tasks: An observable array holding initial tasks.
  • newTaskTitle: An observable to capture the new task title which input.
  • addTask: A function to add a new task to the tasks array when the "Add Task" button is clicked or the enter key is pressed after inputting a new task.
  • removeTask: A function that removes a task from the tasks array when the "Remove" button is clicked.

Output-

answer 6518922706124540

 

Also, Read: How does Knockout.js handle routing in single-page applications (SPA)?

 

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