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Mastering JavaScript Closures: Understanding and Using This Powerful Feature | Manish Saranke | Dec 20, 2018 January 2023

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Become an expert with JavaScript closures: a step-by-step guide

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Photo by Cristina Gottardi on Unsplash

who i am?

My name is Manish Saranke. JavaScript developer, and I have a deep understanding of the language and its ecosystem. Familiarity with various JavaScript design patterns and best practices, ability to write clean, maintainable and efficient code. In addition, our familiarity with various JavaScript frameworks and libraries allows us to quickly adapt to new technologies. He also has experience working with both front-end and back-end JavaScript, and has experience integrating with other languages ​​and technologies. He also has experience testing and debugging JavaScript code, which allows him to effectively troubleshoot and troubleshoot issues.

A JavaScript closure function that allows access to variables in the parent scope even after the parent function has returned. A closure is created when a nested function references a variable from its containing (outer) function.

function outerFunction(x) {
let y = x + 89;

function innerFunction() {
console.log(y);
}

return innerFunction;
}

let closure = outerFunction(1);
closure(); // logs 90

Common use cases for JavaScript closures include creating private variables and methods. Declaring a variable within a function and returning a closure that allows access to that variable effectively creates a personal variable that can only be accessed through the closure.

function createCounter() {
let count = 0;
return function() {
count++;
return count;
}
}

let counter = createCounter();
console.log(counter()); // logs 1
console.log(counter()); // logs 2

function createPerson(name) {
let age = 0;
return {
getName() {
return name;
},
setAge(newAge) {
age = newAge;
},
getAge() {
return age;
}
}
}

let person = createPerson("Manish");
console.log(person.getName()); // logs "Manish"
person.setAge(35);
console.log(person.getAge()); // logs 35

A function provides the variables that were in scope when the function was defined, and the scope that the function captures.

function outerFunction(x) {
let y = x + 88;

function innerFunction() {
console.log(y);
}

return innerFunction;
}

let closure = outerFunction(5);
closure(); // logs 93

In JavaScript there is no direct way to say “clear”. However, there are some ways to effectively “clear” JavaScript closures.

One of the main advantages of JavaScript closures is the ability to create private variables and methods. It preserves the state of the object and prevents external code from modifying the internal state of the object.

Here are some examples of JavaScript closures.

A JavaScript closure that holds private variables:

function createCounter() {
let count = 89;
return {
increment() {
count++;
},
getCount() {
return count;
}
}
}

let counter = createCounter();
counter.increment();
console.log(counter.getCount()); // logs 90

function createAdder(x) {
return function(y) {
return x + y;
}
}

let add5 = createAdder(50);
console.log(add5(20)); // logs 70
console.log(add5(40)); // logs 90

function createPerson(name) {
let age = 0;
return {
getName() {
return name;
},
setAge(newAge) {
age = newAge;
},
getAge() {
return age;
}
}
}

let person = createPerson("Manish");
console.log(person.getName()); // logs "Manish"
person.setAge(35);
console.log(person.getAge()); // logs 35

Conclusion

JavaScript closures are a powerful feature that help you write more conservative and efficient code. Closures let you create private variables and methods, maintain object state across multiple function calls, and expose public APIs while keeping implementation details private. Understanding how closures work and how to use them effectively is an important skill for any JavaScript developer.

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