Fundamentals of Javascript - Part 2(Why should you use let instead of var keyword)
Hello, curious stranger on the internet, today we are going to cover why let and const keyword is preferred over var keyword in Javascript.
In the first part of fundamentals of Javascript, we covered features of Javascript and how to declare variables using let and const keywords.
Let's continue our journey to deep dive into the Javascript world from that point.
The var keyword
In addition to declaring variables using let and const, there is another way to declare variables using the var keyword.
A variable can be declared using the var keyword as shown below:-
var studentName = "Joe";
console.log("Student name is", studentName);
//Output:- Student name is Joe
However, using the let and const keyword is much more preferable to using the var keyword in Javascript. One of the reasons for this is because variable declared using the var keyword can be redeclared using the same name which can lead to a lot of bugs in the code.
Consider the example below:-
var studentName = "Joe";
console.log("Student name is", studentName);
var studentName = "John";
console.log("Student name now is", studentName);
/* Output:-
Student name is Joe
Student name now is John
*/
In the above example, the studentName variable was declared again with a new value without any error. This can lead to bugs while coding. For example, if a person x is using the studentName variable in their file and a person y is using the same variable studentName in their code. The value of the studentName variable will not remain deterministic and can have incorrect values during final program execution.
If we try to do a similar thing with the let keyword this will be the output:-
let studentName = "Joe";
console.log("Student name is", studentName);
let studentName = "John";
console.log("Student name now is", studentName);
/*Output:-
SyntaxError: Identifier 'studentName' has already been declared
*/
In the case of the let keyword, reuse of the same variable name again is not allowed due to which each variable used in the code has a deterministic value. This prevents any unnecessary bugs to enter into our code.
This is one of the reasons why we make use of the let or const keyword instead of the var keyword in Javascript currently.
We will continue learning more about Javascript language in the upcoming articles in the series. I hope you found the article useful.
Which is your favourite feature of Javascript language? Do share it in the comments below.
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