Reactive state management is a core feature of a.js, enabling developers to create dynamic user interfaces with minimal effort. By leveraging JavaScript proxies and the declarative nature of custom tags, a.js simplifies the process of managing and reacting to changes in application state.
<let> and watch constructs to simplify reactive state declaration.Watched variables are declared using the <let> tag, enabling automatic tracking of changes. These variables are wrapped in JavaScript proxies, allowing for seamless reactivity. Note that variable names in <let> must contain a dot (e.g., counters.count). Initialization should occur outside the <let> declaration.
<a-closure>
<let>
global watched counters.count;
</let>
counters.count = 0;
currentElement.addEventListener('click', () => {
counters.count++;
});
{(<div>${counters.count}</div>)}
</a-closure>
In this example, the counters.count variable is watched, and changes to its value can trigger reactive updates in the UI or dependent logic.
Reactive expressions are computations or logic that automatically re-evaluate when their dependencies change. They can be defined using the watch function.
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<let>
global watched values.x;
global watched values.y;
</let>
values.x = 10;
values.y = 20;
const watcher = watch(() => {
console.log('Sum:', values.x + values.y);
});
watcher.suspend = true; // Temporarily suspend watching
watcher.suspend = false; // Resume watching
When either values.x or values.y changes, the expression inside watch is re-evaluated, and the new sum is logged to the console. By toggling the suspend property, developers can control when the watcher reacts.
a.js employs fine-grained dependency tracking to optimize reactivity. Only the parts of the DOM or logic that depend on updated variables are re-evaluated, ensuring efficient updates.
The unwatch function creates a deproxified version of a root watched variable. This unwatched version does not trigger observations inside a watch function, allowing for static access to a variable's value without reactive behavior.
<a-closure>
<let>
global watched data.value;
</let>
data.value = 42;
const staticData = unwatch(data);
watch(() => {
console.log(staticData.value); // This will not trigger when data.value updates
});
In this example, staticData remains a static copy of data and does not participate in the reactivity system, but any update to data.value will be reflected in staticData.value and any update to staticData.value be reflected to data.value (and thus would trigger watched data.value)
Reactive variables can be scoped to specific levels (e.g., global, local, nsGlobal). This ensures that changes to variables only affect the intended parts of the application.
<a-closure>
<let>
global watched app.globalValue;
local watched app.localValue;
</let>
app.globalValue = 42;
app.localValue = 'hello';
watch(() => {
console.log('Global:', app.globalValue);
console.log('Local:', app.localValue);
});
</a-closure>
a.js intelligently batches updates to minimize redundant computations or DOM changes. Multiple changes within the same execution context are applied together.
<a-closure>
<let>
global watched counters.a;
global watched counters.b;
</let>
counters.a = 1;
counters.b = 2;
watch(() => {
console.log('Sum:', counters.a + counters.b);
});
// Batch changes
counters.a = 10;
counters.b = 20;
</a-closure>
In this example, the reactive expression recalculates only once after both counters.a and counters.b are updated.
unwatch for Static Access: Use unwatch to create static versions of reactive variables when needed.suspend property or unwatch to manage unused reactive logic.<let>: Declare variables in <let> without initialization, and assign their values afterward.By understanding and applying these constructs, developers can create highly efficient and dynamic interfaces using a.js's reactive state management.
Event handling in a.js is designed to simplify interaction management by providing a reactive, declarative approach to custom events and event listeners. This system ensures seamless integration between dynamic DOM updates and user-triggered events, supporting modularity and scalability in application development.
Declarative Syntax:
<a-closure> tag simplifies managing interactive behaviors.Reactivity:
Custom Events:
user-logged-in event from a login form and listening for it in a parent container.Scoped and Modular:
Event Delegation:
Event listeners in a.js can be attached directly within component markup using the native onevent syntax, similar to standard JavaScript.
<a-closure>
<let>
global app.handleClick;
</let>
app.handleClick = function(event) {
console.log('Button clicked:', event.target);
};
{(<button onclick="app.handleClick(event)">Click Me</button>)}
</a-closure>
In this example, clicking the button triggers the handleClick function.
Dynamic event listeners enable the behavior of events to change based on application state.
<a-closure>
<let>
global app.buttonAction;
</let>
app.buttonAction = function(event) {
console.log('Default action');
};
{(<button onclick="app.buttonAction(event)">Dynamic Button</button>)}
app.buttonAction = function(event) {
console.log('Updated action');
};
</a-closure>
The app.buttonAction function dynamically updates its behavior without requiring reattachment.
Custom events allow components to emit application-specific events, enhancing inter-component communication.
<a-closure>
{(<button onclick="currentElement.dispatchEvent(new CustomEvent('customEvent', { detail: { data: 'Example' } }))">
Emit Event
</button>)}
currentElement.addEventListener('customEvent', function(event) {
console.log('Received custom event:', event.detail.data);
});
</a-closure>
Here, clicking the button emits a customEvent that other parts of the application can listen for.
Event delegation optimizes performance by attaching a single listener to a parent element to handle events for its children dynamically.
<a-closure>
<let>
global app.handleListClick;
</let>
app.handleListClick = function(event) {
if (event.target.tagName === 'LI') {
console.log('Clicked item ID:', event.target.dataset.id);
}
};
{(<ul onclick="app.handleListClick(event)">
<li data-id="1">Item 1</li>
<li data-id="2">Item 2</li>
<li data-id="3">Item 3</li>
</ul>)}
</a-closure>
This approach reduces memory usage and improves performance, particularly for dynamically generated lists.
By understanding and using these patterns, developers can build highly interactive and maintainable applications with a.js.