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When should you use "var", "let", or "const" in JavaScript code [duplicate]

stackoverflow.com › questions › 76010295 › when-should-you-use-var-let-or-const-in-javascript-code

In my opinion nowadays it is better to use let and const.

According to the ES6 standard, these options are more convenient with their scope. Both give us the so-called block scope. This means that the scope of their use can be limited to a block of code, such as a for loop or an if expression. This gives the developer more flexibility in choosing the scopes of variables.

In addition, if we consider these options, then you will not be able to change the variable declared with const, unlike var and let.

Generally speaking, let and const are often used now, depending on the need.

Answer from nixanosize on Stack Overflow

reddit.com › r/learnjavascript › difference between var, let and const

r/learnjavascript on Reddit: Difference between var, let and const

March 28, 2022 -

Hi everyone!

I'm pretty new to web development and have started to read a little bit about javascript. Right now I'm trying to learn how to declare a function but realized that there is different ways to do this using var, let or const. Since I'm new to this, most of the explanation on the internet is pretty advanced to understand atm, so could anyone explain the differences for me very short short and easy, alternatively give me a link that explain it in pretty easy terms?

Thanks in advance!

(Edit: Thank you so much for the answers, rly appreciate it!)

Top answer

1 of 5

Using the function keyword creates a function declaration. Function declarations are hoisted to the top of the scope, thus the following code works fine: add(1, 2) function add (a, b) { return a + b } There are readability advantages to using the function keyword as it clearly communicates that this is a function. We can also create an anonymous function expression and, because functions in JavaScript are first class citizens, assign a function to a named variable with let, const or var. Keep in mind though, variables declared with let and const are hoisted, but not initialized with a value. Whereas variables declared with var are hoisted and initialized with the value undefined. So because add is invoked prior to it's initialization in the code below we encounter an error. With let/const: add(1, 2) // Reference error - cannot access 'add' before initialization const add = function (a, b) { return a + b } With var: add(1, 2) // Type error - 'add' is not a function (as it is initialized as undefined when hoisted) var add = function (a, b) { return a + b } If you're assigning a function to a variable I can't think of any situation where you wouldn't use const. Functions should always be pure and immutable whenever possible. Given a certain input, the output should always be consistently the same. Using const protects you from accidentally reassigning a variable containing a function expression. Compare this to use of the function keyword, which allows you to declare a named function twice, overiding the previous: function add (a, b) { return a + b } function add (a, b) { return a - b } add(2, 1) // 1 This is a disadvantage of function declarations versus expressions. Provided you understand the pros/cons and how hoisting works, it is really personal choice whether you prefer function declarations versus expressions.

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All you need to remember is that var should never be used in modern JavaScript. Functions should either use the function keyword or const (with arrow functions). Objects/arrays should always be const. Just always use const until you can’t.

Stack Overflow

stackoverflow.com › questions › 76010295 › when-should-you-use-var-let-or-const-in-javascript-code

When should you use "var", "let", or "const" in JavaScript code - Stack Overflow

Top answer

1 of 1

In my opinion nowadays it is better to use let and const.

In addition, if we consider these options, then you will not be able to change the variable declared with const, unlike var and let.

Generally speaking, let and const are often used now, depending on the need.

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