Learn Closures In 7 Minutes

Summary

In this video, Kyle from Web Dev Simplified explains the concept of closures in JavaScript. He begins with a simple example, demonstrating how variables outside a function can be accessed within it, forming a closure. Kyle illustrates this with an example where a function accesses a global variable, showing how the variable's value updates dynamically. He then delves into more common use cases, such as functions within functions and how closures retain access to variables even after the outer function has executed. The video concludes with practical applications of closures using fetch and promises in JavaScript.

Takeaways

• 😀 Closures in JavaScript allow functions to access variables from their outer scope even after the outer function has finished executing.
• 🎯 The video introduces closures with a simple example involving a 'printName' function and a global variable 'myName'.
• 🌟 The script demonstrates that closures are not just about accessing the value at the time of function creation, but the current live value of the variable.
• 🔄 It shows that changing the value of a variable after a function has been defined can still affect the output when the function is called later.
• 📚 The video explains that every scope in JavaScript, including the entire file and any functions within it, has access to the outer scope.
• 🏢 The concept of closures is further illustrated with an 'outer function' returning an 'inner function', highlighting how the inner function retains access to the outer variable.
• 🔑 The script clarifies that even when the outer function's execution is complete, the inner function maintains access to its variables due to closures.
• 🛠️ Common use cases of closures are shown, such as using functions within functions to maintain access to scoped variables, which is useful in asynchronous operations like fetching data.
• 🌐 An example with 'fetch' is given to explain how closures can be used to access variables defined in an outer function within a callback function of a promise.
• 👨‍🏫 The video aims to simplify the concept of closures and encourage viewers to explore more through subscribing to the channel for related content.
• 📈 The presenter emphasizes the practical applications of closures, particularly in scenarios involving asynchronous operations and callbacks.

Q & A

What is the main topic of the video?

The main topic of the video is explaining the concept of closures in JavaScript.

What is the presenter's name and the purpose of his channel?

The presenter's name is Kyle, and the purpose of his channel is to simplify web development concepts for the audience.

Why is the simple JavaScript code with the variable 'myName' and the 'printName' function considered a closure?

The simple JavaScript code is considered a closure because the 'printName' function has access to the 'myName' variable, which is in an outer scope, demonstrating the ability to access external variables within a function.

How does the video demonstrate that closures update with the current live value of a variable?

The video demonstrates this by changing the value of 'myName' from 'Kyle' to 'Joey' and showing that the 'printName' function prints the updated value, indicating that closures capture the current state of the variable at the time of function execution.

What is the difference between a global variable and a variable in a closure?

A global variable is accessible throughout the entire script, while a variable in a closure is accessible only within the function that creates the closure, even after the outer function has finished executing.

Can you give an example of a more common use case of closures mentioned in the video?

A more common use case of closures mentioned in the video is when a function (outer function) returns another function (inner function), and the inner function has access to the outer function's variables.

How does the video explain the scope concept in relation to closures?

The video explains that in JavaScript, every scope, such as the entire file or a function, has access to everything in its outer scope. This is how closures work, allowing functions to access variables from their parent scopes.

What happens to the outer variable after the outer function has finished executing in the context of closures?

In the context of closures, even after the outer function has finished executing, the inner function retains access to the outer variable because it 'remembers' the outer variable's value at the time of its creation.

Why are closures particularly useful in asynchronous operations like fetching data with Axios or fetch?

Closures are particularly useful in asynchronous operations because they allow the inner function, which is called after the outer function has completed, to still have access to the outer function's scope, including variables that are needed to process the data once the promise resolves.

Can you provide an example of how closures are used with asynchronous functions like fetch?

The video provides an example where an outer function is defined to fetch a URL, and the fetch function's '.then()' method contains an inner function that has access to the outer function's variables, such as the URL, even after the outer function has finished executing.

What is the key takeaway from the video about closures?

The key takeaway from the video is that closures in JavaScript allow an inner function to have access to the variables and scope of an outer function, even after the outer function has finished executing.