π€― Under the hood of the JavaScript series!
5οΈβ£ HOISTING & TDZ(Temporal Dead Zone) in JavaScript?
A Threadπ§΅π
5οΈβ£ HOISTING & TDZ(Temporal Dead Zone) in JavaScript?
A Threadπ§΅π
β Before going deep dive into this topic there is a prerequisite for this topic which is "scope" in javascript.
π You can learn it from hereπ
π You can learn it from hereπ
π What is HOISTING?
β HOISTING is a JavaScript behavior in which a function or variable can be accessed or used before the declaration.
β Or, a JavaScript variable/function can be used before being declared.
β HOISTING is a JavaScript behavior in which a function or variable can be accessed or used before the declaration.
β Or, a JavaScript variable/function can be used before being declared.
β But it is not going to work with let and const keywords.
β Hoisting only works with the "var" keyword.
β Javascript "initialization" is not hoisted but "declarations" are hoisted.
β Hoisting only works with the "var" keyword.
β Javascript "initialization" is not hoisted but "declarations" are hoisted.
β See in this example, the only declaration is hoisted not the value.
β Variable declared with "var" keyword is initialized with "undefined" value by default.
β The function is also hoisted with only the "var" keyword but not initialized.
β Variable declared with "var" keyword is initialized with "undefined" value by default.
β The function is also hoisted with only the "var" keyword but not initialized.
β But it will not work with "let" and "const" keywords.
β You will get a ReferenceError because of TDZ(Temporal Dead Zone).
β let and const are hoisted but not initialized with a default value like the "var" keyword that's why it gives an error.
β You will get a ReferenceError because of TDZ(Temporal Dead Zone).
β let and const are hoisted but not initialized with a default value like the "var" keyword that's why it gives an error.
π Here is some example of the function.
β In the arrow function, we get an error as "sumArrow is not a function" because the value of the "sumArrow" function is undefined.
β In the arrow function, we get an error as "sumArrow is not a function" because the value of the "sumArrow" function is undefined.
β So we can't call like "undefined(10, 20)"
π What is TDZ(Temporal Dead Zone)?
β That means we can not access a variable or function before its declaration.
β This works only with the "let" and "const" keywords.
β An area or zone which is temporarily inactive for a particular variable or function.
β That means we can not access a variable or function before its declaration.
β This works only with the "let" and "const" keywords.
β An area or zone which is temporarily inactive for a particular variable or function.
β The above image shows that the red box is in the "temporal dead zone" of the "TDZ" variable.
β That means it can be accessible before line number 6.
β It will be accessible starting from the line where it is defined.
β Otherwise, we will get a ReferenceError.
β That means it can be accessible before line number 6.
β It will be accessible starting from the line where it is defined.
β Otherwise, we will get a ReferenceError.
That's all for now, we will meet in the next threadπ
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But if you like make sure to:
1. Follow me @ATechAjay
2. Retweet the first tweet.
3. Turn on the notification to never miss these amazing tweets.
Thank you so much for staying to the end of this thread.
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