Close Menu
    Explore the coolest frontend learning platform !
    Visit NamasteDev
    Wednesday, April 2

    Understanding how var, const, let and functions are hoisted

    Chosen Topic 760 Comments3 Mins ReadIrene agigibaBy

    Have you heard of hoisting?, and might be wondering what it is right, or you probably got an error and they told you it was as a result of hoisting right?

    Anyways I am here to get you through it.

    PREREQUISITE KNOWLEDGE:

    JavaScript is a synchronous single threaded language.

    Synchronous means it executes code in the order in which they were placed on the script (from the top to bottom), it executes the code from line 1, then line 2 and so on.

    Single threaded means it only does one thing at a time, it does not multitask, it fully executes a line of code before it continues to the next line, it cannot be executing the code in line 3 at the same time the code in line 4.

    So in short, synchronous single-threaded means it executes one line of code at a time in the order they appear on the script (from top to bottom).

    HOISTING is storing of variables and functions in the variable environment or memory of an execution context before execution. 

    Before JavaScript starts executing your code, it stores it memory first

    1. Variables stored with “var” keywords are assigned “undefined” in memory during hoisting. Hence if you try to access them before they are executed you will get undefined.

    NOTE: The debugger is turned on to pause to the code from executing at specific points so you can notice what happens within the code and the memory

    Notice what is assigned to “a” in the global memory before the line var a = “JavaScript” was executed.

    2. Variables stored with “const” and “let” keywords assigned “<value unavailable>” are stored in the Temporal Dead Zone (TDZ) , a separate section within the global memory. When you try to access them before they are executed, you get an error “ReferenceError: Cannot access ‘b’ before initialization”.

    Notice variables “a” and “b” are saved in “Script” and not “Global” and they are assigned “<value unavailable>”. This only happens before line const b =”Hoisting” and let c = “John” are executed.

    Classes are also hoisted like “const” and “let”. You cannot initialize a class before executing it else you will get an error

    Example: 

    3. Functions are stored with a reference to the entire function code, hence you can invoke or access them before they are executed.

    Notice here that the function labeled “arr” has been saved in memory before it is executed, the debugger is placed on the first line which means it pauses the code execution.

    Hence you can easily use or print or invoke a function before it is executed in the next line of code. 

    Keep Reading

    View 760 Comments

    760 Comments

    4. Cheap Seo Techniques on

      When I originally commented I clicked the „Notify me when new comments are added” checkbox and now each time acomment is added I get several emails with the same comment.Is there any way you can remove me from that service?Bless you!

      Reply
    14. Tang like Facebook on

      Heya! I just wanted to ask if you ever have any problems with hackers? My last blog (wordpress) was hacked and I ended up losing several weeks of hard work due to no data backup. Do you have any solutions to protect against hackers?

      Reply
    15. jav porn on

      🎮แหล่งรวมคาสิโนออนไลน์🎮💥รวมเกมค่ายดังมากมาย💥✅ฝาก-ถอนไม่มีขั้นต่ำ.⏱✅รวดเร็วทันใจด้วยระบบเติมเงินออโต้🔥ติดต่อสอบถามเพิ่มเติม หรือ สมัครสมาชิก 🔥

      Reply
    17. togel4d on

      Hey There. I found your blog utilizing msn. That may be a rather well penned article. I’ll make sure to bookmark it and return to browse excess of your handy info. Thanks to the article. I will certainly return.

      Reply
    20. Carie on

      Thanks for every other excellent article. Where else may anyone get that kind of info in such a perfect method of writing? I’ve a presentation next week, and I am at the look for such info.

      Reply
    23. promo code on

      What brought this level of popularity to him was that it absolutely was aactivity built with terrific effort and hard work.Free Account – New Free Accounts And Passwordsfree accounts

      Reply
    145. see more on

      I haven’t checked in here for a while as I thought it was getting boring, but the last several posts are great quality so I guess I’ll add you back to my daily bloglist. You deserve it my friend 🙂

      Reply
    160. Elvin Emami on

      Greetings! I know this is somewhat off topic but I was wondering which blog platform are you using for this website? I’m getting tired of WordPress because I’ve had issues with hackers and I’m looking at alternatives for another platform. I would be fantastic if you could point me in the direction of a good platform.

      Reply
    161. Kimber Olvey on

      Hey there! I’m at work surfing around your blog from my new apple iphone! Just wanted to say I love reading through your blog and look forward to all your posts! Carry on the superb work!

      Reply
    173. Stephan Larmer on

      Does your website have a contact page? I’m having trouble locating it but, I’d like to shoot you an e-mail. I’ve got some recommendations for your blog you might be interested in hearing. Either way, great blog and I look forward to seeing it improve over time.

      Reply
    178. Raeann Penski on

      This is the best blog for anybody who desires to seek out out about this topic. You understand a lot its virtually onerous to argue with you (not that I truly would want…HaHa). You definitely put a new spin on a subject thats been written about for years. Nice stuff, simply nice!

      Reply
    189. Sushi Swap on

      nice article ave a look at my site “https://www.newsbreak.com/crypto-space-hub-313321940/3799652652916-top-crypto-investments-in-2025-bitcoin-ai-projects-tokenized-assets”

      Reply
    203. Ula Burgees on

      Definitely imagine that that you said. Your favorite reason appeared to be on the web the simplest factor to be aware of. I say to you, I certainly get irked whilst folks consider concerns that they just do not realize about. You managed to hit the nail upon the highest as neatly as defined out the entire thing with no need side effect , other folks can take a signal. Will probably be back to get more. Thank you

      Reply
    225. SpookySwap on

      SpookySwap is a next-generation decentralized exchange (DEX) built on the lightning-fast Fantom Opera blockchain. Designed for efficiency, security, and low-cost transactions, SpookySwap empowers users to trade, stake, and earn without relying on centralized intermediaries. Its seamless user experience and robust features make it a key player in the expanding world of decentralized finance (DeFi).

      Reply
    273. Tang follow Facebook on

      I like the helpful information you provide for your articles.I’ll bookmark your blog and take a look at once more right here regularly.I’m slightly sure I’ll be told lots of new stuff proper here!Good luck for the next!

      Reply
    367. to read more on

      Hey there! This post could not be written any better!Reading through this post reminds me of my old room mate!He always kept talking about this. I will forward this write-up to him.Fairly certain he will have a good read. Many thanks for sharing!

      Reply
    478. fichajes de fútbol on

      wonderful post, very informative. I wonder why the other experts of this sector do not notice this. You must continue your writing. I am confident, you’ve a great readers’ base already!

      Reply
    512. click here on

      It’s really a great and helpful piece of info. I am happy that you shared this helpful info with us. Please keep us informed like this. Thanks for sharing.

      Reply
    580. Jessevox on

      Играйте РЅР° деньги Рё получайте удовольствиe.: balloon казино – balloon казино официальный сайт

      Reply
    583. Jessevox on

      Р’ казино всегда есть что-то РЅРѕРІРѕРµ.: balloon игра – balloon казино официальный сайт

      Reply
    584. Martyhap on

      Присоединяйтесь Рє игрокам РЅР° автоматах.: balloon game – balloon казино играть

      Reply
    597. Martyhap on

      Автоматы Ballon поднимают настроение каждому.: balloon game – balloon казино

      Reply
    604. SciatiSoothe on

      Hi there! I know this is kinda off topic but I was wondering if you knew where Icould get a captcha plugin for my comment form? I’m using thesame blog platform as yours and I’m having trouble findingone? Thanks a lot!

      Reply
    653. San Xuat Luoi Thep Han on

      Hello are using WordPress for your blog platform? I’m new to the blog world but I’m trying to get started and create my own. Do you need any coding knowledge to make your own blog? Any help would be greatly appreciated!

      Reply
    699. qua tang doanh nghiep on

      After I originally commented I clicked the -Notify me when new comments are added- checkbox and now every time a remark is added I get 4 emails with the identical comment. Is there any approach you may take away me from that service? Thanks!

      Reply
    703. see more on

      Hi! This is my first visit to your blog! We are a collection of volunteers and starting a new project in a community in the same niche. Your blog provided us beneficial information to work on. You have done a wonderful job!

      Reply
    705. click for more on

      It’s actually a nice and helpful piece of information. I am glad that you simply sharedthis helpful information with us. Please keep us up to date likethis. Thank you for sharing.My blog – skin cells

      Reply
    716. buy ssn for cashapp on

      Thanks , I have just been searching for info about this subject for a while and yours is the greatest I’ve came upon so far. However, what in regards to the bottom line? Are you certain about the source?

      Reply
    Leave A Reply

    Demo

    Courses

    Community

    Contact Us