Web Development Articles
PHP $this, self and parent operators
Sometimes different aspects of object oriented programming can be a little confusing if you can’t picture a use case for them. Three class operators in PHP where usage can be a little confusing at times are $this, self and parent. In this article I will try to break things down and maybe you can see where you can use this in your code. Ok so let’s begin.
1. $this
- Refers to the current object instance.
- You use $this when you want to access properties or methods of the current object.
Example:
class Animal {
public $name;
public function setName($name) {
$this->name = $name; // "this object’s" name
}
public function getName() {
return $this->name; // returns "this object’s" name
}
}
$dog = new Animal();
$dog->setName("Buddy");
echo $dog->getName(); // Output: Buddy
2. self
- Refers to the current class itself, not the instance.
- Used for static methods and static properties.
- Does not depend on an object ($this is not available in static context).
Example:
class MathHelper {
public static $pi = 3.14159;
public static function circleArea($radius) {
return self::$pi * $radius * $radius; // accessing static property with self
}
}
echo MathHelper::circleArea(5); // Output: 78.53975
3. parent
- Refers to the immediate parent class.
- Used when you want to access a method or constructor from the parent class that is overridden in the child.
Example:
class Animal {
public function makeSound() {
return "Some generic animal sound";
}
}
class Dog extends Animal {
public function makeSound() {
// Call parent method, then add more
return parent::makeSound() . " and Woof!";
}
}
$dog = new Dog();
echo $dog->makeSound(); // Output: Some generic animal sound and Woof!
Now to summarize:
- $this refers to an instance of the class. It isn’t available in a static context, therefore cannot be used within a static class function.
- The self:: operator refers to the class-level property. It is used in a static context and refers to the actual class itself.
- The parent:: operator calls the overridden method from the parent class. It’s used in inheritance typically to call an overwritten method on the parent class.
Here is a really good example that should help you concieve these concepts and clear up any confusion.
class Animal {
public $name;
public static $kingdom = "Animalia";
public function __construct($name) {
$this->name = $name; // instance reference
}
public function describe() {
return "I am an animal named {$this->name}.";
}
public static function getKingdom() {
return "Kingdom: " . self::$kingdom; // static reference
}
}
class Dog extends Animal {
public function describe() {
// Use parent to get base description
$base = parent::describe();
// Add Dog-specific description
return $base . " I am also a dog that says Woof!";
}
public function introduce() {
// `$this` calls instance method
return $this->describe();
}
public static function getInfo() {
// `self` calls static property from this class (or parent if not overridden)
return "Dogs belong to " . self::$kingdom;
}
}
// ------------------- USAGE -------------------
// Create an object
$dog = new Dog("Buddy");
// $this -> instance reference
echo $dog->introduce();
// Output: I am an animal named Buddy. I am also a dog that says Woof!
echo "<br>";
// self -> static reference
echo Dog::getInfo();
// Output: Dogs belong to Animalia
echo "<br>";
// parent -> calling parent method inside child
echo $dog->describe();
// Output: I am an animal named Buddy. I am also a dog that says Woof!
echo "<br>";
// static method from parent
echo Animal::getKingdom();
// Output: Kingdom: Animalia
Master JavaScript Asynchronous Programming with Promise.allSettled()
The Promise.allSettled() method is a powerful tool for handling multiple promises in JavaScript. It returns a single Promise that resolves with an array of objects, each representing the outcome of a promise in the input array.
Each outcome object contains a status property, which is either 'fulfilled' or 'rejected'.
- If the status is 'fulfilled', the object will also contain a value property with the resolved value.
- If the status is 'rejected', the object will contain a reason property with the error (typically the value passed to reject).
Key Difference: Promise.allSettled() vs. Promise.all()
Unlike Promise.all(), which immediately rejects if any promise in the iterable is rejected, Promise.allSettled() never short-circuits. It waits for all promises to settle (either fulfill or reject), making it ideal for use cases where you need to know the result of every asynchronous operation, regardless of individual failures. This provides a more robust way for error handling in async/await and promise chains.
When to use Promise.allSettled() in JavaScript?
Use it whenever you need to process the results of multiple independent asynchronous operations and you don't want a single failure to prevent you from handling the others. Common scenarios include making multiple API calls or database queries where individual failures are non-critical.
The following example demonstrates how to use Promise.allSettled() to handle a mix of successful and failed promises.
// Example: Handling multiple API calls or asynchronous tasks
const p1 = new Promise((resolve, reject) => {
setTimeout(resolve, 200, "Data for User 1"); // Simulates a successful API call
});
const p2 = new Promise((resolve, reject) => {
setTimeout(resolve, 200, "Data for User 2"); // Simulates another successful call
});
const p3 = new Promise((resolve, reject) => {
setTimeout(reject, 200, "User 3 not found"); // Simulates a failed API call (e.g., 404)
});
const p4 = new Promise((resolve, reject) => {
setTimeout(reject, 200, "Server error for User 4"); // Simulates a server error (e.g., 500)
});
// Execute all promises and handle results with allSettled
Promise.allSettled([p1, p2, p3, p4])
.then(results => {
console.log("All operations settled:");
results.forEach((result, index) => {
if (result.status === 'fulfilled') {
console.log(`Promise ${index + 1}: Success -`, result.value);
} else {
console.log(`Promise ${index + 1}: Failed -`, result.reason);
}
});
});
// ** CONSOLE OUTPUT **
// All operations settled:
// Promise 1: Success - Data for User 1
// Promise 2: Success - Data for User 2
// Promise 3: Failed - User 3 not found
// Promise 4: Failed - Server error for User 4
JavaScript Self-Invoked Functions (IIFEs)
What is a self-invoked function? (IIFE)
A self-invoked function, also called an Immediately Invoked Function Expression (IIFE) is a Javascript function expression that is invoked immediately after its declaration. A self-invoked function can be a valuable tool for creating isolated scopes and managing variable privacy in javascript applications.
Key aspects of IIFEs:
- IIFEs execute immediately when defined
- Allows creation of private scopes without polluting global namespace
- Return values can be assigned to variables
- Parameters can be passed to IIFEs
Basic syntax:
(function() {
// code here
})();
// OR arrow functions (ES6+)
(() => {
// code here
})();
Why are IIFEs Necessary?
Immediate Execution with Parameters
// Immediately logs provided data
(function(date, location) {
console.log(`Date: ${date.toDateString()}`);
console.log(`Location: ${location}`);
})(new Date(), 'Seattle');
// Immediately logs:
// Date: Thu Oct 16 2025
// Location: Seattle
Avoiding Global Namespace Pollution
// if multiple scripts use the same variable names
// they won't conflict
(function() {
const restaurant = "Dairy Queen";
console.log(user); // "Dairy Queen"
})();
(function() {
const restaurant = "Burger King";
console.log(user); // "Burger King"
})();
Data Privacy/Encapsulation
// Problem: counter value is vulnerable.
var counter = 0;
function increment() {
return ++counter;
}
// FIX: keeps variables private. counterModule isn't directly accessible
const counterModule = (function() {
let count = 0;
return {
increment: function() {
return ++count;
},
decrement: function() {
return --count;
},
getCount: function() {
return count;
}
};
})();
counterModule.count = 100; // WONT WORK!!
// count is not accessible directly
console.log(counterModule.getCount()); // 0
counterModule.increment();
console.log(counterModule.getCount()); // 1
// OUPTUT: 0 1
Module Pattern Implementation
const User = (function() {
let memory = 0;
function add(a, b) {
return a + b;
}
function store(value) {
memory = value;
}
function recall() {
return memory;
}
// Only expose public methods
return {
add: add,
store: store,
recall: recall
};
})();
console.log(Calculator.add(5, 3)); // 8
Calculator.store(10);
console.log(Calculator.recall()); // 10
// memory is private and inaccessible
PHP Access Modifiers (public, private, protected)
In PHP Object-Oriented programming, public, private, and protected are access modifiers (visibility keywords) used to control how properties (variables) and methods (functions) of a class can be accessed.
They are important in Object-Oriented Programming (OOP) because they enforce encapsulation (controlling how data is exposed and used).
Public
Members declared public can be accessed from inside the class, outside of the class and by subclasses (child classes). If no visibility is specified on a property the default will be public.
class Car {
public $brand;
public function setBrand($brand) {
$this->brand = $brand; // accessible inside the class
}
}
$car = new Car();
$car->brand = "Toyota"; // accessible outside the class
echo $car->brand; // Output: Toyota
Private
Members declared private can only be accessed inside of the class that defines them. They cannot be accessed from outside the class or by subclasses.
class Car {
private $engineNumber;
public function setEngineNumber($num) {
$this->engineNumber = $num; // accessible inside the class
}
public function getEngineNumber() {
return $this->engineNumber; // allowed via public method
}
}
$car = new Car();
$car->setEngineNumber("ENG123");
// echo $car->engineNumber; ERROR: Cannot access private property
echo $car->getEngineNumber(); // Output: ENG123
Protected
Members declared protected can be accessed inside of the class, in child(sub) classes that inherit from it. They cannot be accessed directly from outside of the class… only subclasses.
class Vehicle {
protected $type = "Generic Vehicle";
protected function getType() {
return $this->type;
}
}
class Car extends Vehicle {
public function showType() {
return $this->getType(); // accessible in child class
}
}
$car = new Car();
// echo $car->type; ERROR: Cannot access protected property
echo $car->showType(); // Output: Generic Vehicle
Solve Vue.js Component Overload with Parent-Child Patterns
Has your Vue component become a tangled mess? Too much template markup, too many responsibilities, and decreasing maintainability.
Well the solution is to use component composition with parent-child relationships that Vue provides.
In this tutorial, you'll learn to:
1. Refactor effectively breaking up monolithic components into focused children
2. Pass data gracefully using props to send data from parent to child
3. Handle child events by capturing custom events emitted by child components
4. Maintain clean data flow by establishing predictable communication between components
See a real-world example where a parent component delegates UI to a specialized Toolbar child, creating cleaner code and better separation of concerns.
Parent Component:
<template>
<div class="parent-component">
<h2>Evaluate Product</h2>
<Toolbar :message="message" @evaluate-product="evaluate" />
<div class="parent-data">
<p>Total Likes: {{ total.likes }}</p>
<p>Total Dislikes: {{ total.dislikes }}</p>
<p v-if="action">Last Action: {{ action }}</p>
</div>
</div>
</template>
<script>
import Toolbar from './Toolbar.vue';
export default {
name: 'EvaluateComponent',
components: {
Toolbar
},
data(){
return {
total: {
likes: 0,
dislikes: 0
},
message: '',
action: null,
messageTimeout: null
}
},
methods:{
evaluate(task) {
// Clear previous timeout
if (this.messageTimeout) {
clearTimeout(this.messageTimeout);
}
switch(task) {
case 'like':
this.total.likes++;
this.message = "Like incremented successfully!";
this.action = 'like';
break;
case 'dislike':
this.total.dislikes++;
this.message = "Dislike incremented successfully!";
this.action = 'dislike';
break;
}
// Auto-clear message after 3 seconds
this.messageTimeout = setTimeout(() => {
this.message = '';
}, 3000);
}
},
beforeDestroy() {
// Clean up timeout when component is destroyed
if (this.messageTimeout) {
clearTimeout(this.messageTimeout);
}
}
}
</script>
Child Component (Toolbar tag in the parent):
<template>
<div class="child-component">
<div class="message" v-if="messageSet">{{ message }}</div>
<button @click="performEvaluate('like')">Like</button>
<button @click="performEvaluate('dislike')">Dislike</button>
</div>
</template>
<script>
export default {
props: {
message: {
type: String,
default: ''
}
},
data() {
return {
// You can add data properties here if needed
}
},
emits: ['evaluate-product'],
computed: {
messageSet() {
return this.message.length > 0;
}
},
methods: {
performEvaluate(evaluation) {
this.$emit('evaluate-product', evaluation);
}
}
}
</script>
Understanding JavaScript Promise.all()
Promise.all() takes an array of promises and returns a single promise that fulfills when all input promises have been fulfilled, or rejects immediately if any of the input promises reject.
Basic Usage:
// resolve promise1
const promise1 = new Promise((resolve, reject) => {
setTimeout(resolve, 200, "King");
});
// resolve promise2
const promise2 = new Promise((resolve, reject) => {
setTimeout(resolve, 100, "Queen");
});
// Notice that all promises supplied must resolve or an error is
// thrown and the promise will be handled in catch()
Promise.all([promise1, promise2]).then(
(fulfilled) => {
console.log(`All fulfilled: ${fulfilled.length}`);
console.log(fulfilled)
}
).catch(e => console.log(e));
// All fulfilled:
// [ 'King', 'Queen' ]
All Promises Must Resolve:
If any Promise in the chain is rejected, a Promise error is returned and will be handled with Promise.catch(). It’s important to get into a habit of providing a Promise.catch() to handle any rejected results.
// All promises are resolved successfully! An array with resolved results
// from each of the fulfilled promises is provided to the chained
// Promise.then(x => console.log(x)) method.
Promise.all([
Promise.resolve("Success 1"),
Promise.resolve("Success 2"),
Promise.resolve("Success 3")
]).then(results => {
console.log(results); // ['Success 1', 'Success 2', 'Success 3']
});
Handling Rejections Gracefully:
// One promise rejects - all others are ignored
const promise1 = new Promise((resolve, reject) => {
setTimeout(resolve, 200, "King");
});
const promise2 = new Promise((resolve, reject) => {
setTimeout(reject, 100, "Queen rejected!");
});
Promise.all([promise1, promise2])
.then((fulfilled) => {
// This will NOT execute
console.log("All fulfilled");
})
.catch(e => {
console.log("Error:", e); // "Error: Queen rejected!"
});
// Output: "Error: Queen rejected!"
Order of Preservation:
A results array is returned ordered in the sequence in which the promise fulfills in the list. All promises are executed in parallel. The first promise to resolve will be the first element of the return array. Notice in this example the first promise in the supplied promises array is actually the last promise in the return array of resolved promises.
// Order of Preservation
// Results maintain the same order as input promises
Promise.all([
new Promise((resolve, reject) => {
setTimeout(resolve, 100, "First");
}),
Promise.resolve("Second"),
Promise.resolve("Third")
])
.then(results => {
console.log(results[0]); // "Second"
console.log(results[1]); // "Third"
console.log(results[2]); // "First"
});
Immediate Rejection:
Notice slowResolve below continues executing but the results are ignored. It’s handled in Promise.catch()
// If any promise rejects, Promise.all immediately rejects
// without waiting for other promises
const fastResolve = new Promise(resolve =>
setTimeout(resolve, 100, "Fast")
);
const slowResolve = new Promise(resolve =>
setTimeout(resolve, 500, "Slow")
);
const fastReject = new Promise((resolve, reject) =>
setTimeout(reject, 50, "Rejected!")
);
Promise.all([fastResolve, slowResolve, fastReject])
.then(results => {
// Never executes
console.log("Success:", results);
})
.catch(error => {
console.log("Caught:", error); // "Caught: Rejected!"
// Both fastResolve and slowResolve continue executing but its result are ignored
});
Always Include Proper Error Handling:
Promise.all([apiCall1(), apiCall2(), apiCall3()])
.then(([result1, result2, result3]) => {
// Process all results
console.log("All API calls succeeded");
})
.catch(error => {
console.error("One or more API calls failed:", error);
// Handle the error appropriately
});
Parallel Processing
It’s perfect for processing multiple API calls in parallel.
const userId = 123;
const api1 = new Promise(resolve => fetch(`/api/users/${userId}`));
const api2 = new Promise(
resolve => fetch(`/api/users/${userId}/posts`)
);
const api3 = new Promise(
resolve => fetch(`/api/users/${userId}/settings`)
);
Promise.all([
api1,
api2,
api2
])
.then(responses => Promise.all(responses.map(r => r.json())))
.then(([user, posts, settings]) => {
console.log("User profile, posts and settings loaded");
// Use all data
})
.catch(error => {
console.error(error);
});
Promise.all() Summary:
1. Promise.all() waits for all promises to resolve or any to reject
2. Order of results matches the input array order
3. Fast failure - rejects immediately on first rejection
4. Always use .catch() to handle potential rejections
5. Perfect for parallel operations that don't depend on each other
If you need different behavior (like waiting for all promises to settle regardless of outcome), checkout Promise.allSettled().
How to use JavaScript Promise catch()
There are a few ways to take advantage of the Promise catch method. The catch() method is run when the Promise is rejected or throws an error. Return value from a Promise is passed forward to the catch() method. Promises can be chained as well. It simply forwards the return value from the chained Promise to the catch method if the Promise is rejected or an error is thrown.
A basic example of using catch() with a Promise reject:
// using Promise.reject
let rejectPromise = new Promise(function(resolve, reject){
reject("promise rejected")
})
function displayCatch(x) {
console.log(x)
}
rejectPromise.catch(x => displayCatch(x))
A basic example of using catch() by throwing an error from the promise:
// throw an error
let promiseError = new Promise(function(resolve, reject){
throw "throw error"
})
function displayCatch(x) {
console.log(x)
}
promiseError.catch(x => displayCatch(x));
Chained promises. Reject or throw error from chained Promise:
let resolvePromise = new Promise(function(resolve, reject) {
setTimeout(resolve, 50, "resolved chained");
})
function resolveDisplay(x) {
console.log(x)
throw "throw error from chained Promise"
}
function displayCatch(x) {
console.log(x)
}
resolvePromise.then(x => resolveDisplay(x)).catch(x => displayCatch(x))