In JavaScript, let and const are used to declare variables. The main difference between them is that variables declared with let can be reassigned new values, while variables declared with const cannot be reassigned after they are initialized.
Here are a few examples:
Using let:
let x = 5;
console.log(x); // Output: 5
x = 6;
console.log(x); // Output: 6
Using const:
const y = 5;
console.log(y); // Output: 5
y = 6; // This will throw an error because y is a constant and cannot be reassigned
In summary, you should use const to declare variables whose values you do not intend to change, and use let for variables that you expect to change in the future.
const is used to declare a constant variable in JavaScript. The variable that is declared with const cannot be reassigned a new value after it is initialized.
Here are a few examples of how to use const:
Declaring a constant variable:
const PI = 3.14;
console.log(PI); // Output: 3.14
Trying to reassign a constant variable:
PI = 3.15; // This will throw an error because PI is a constant and cannot be reassigned
const also used to declare constant objects and array, but the elements of the objects and array can be modified.
const person = {
name: "John",
age: 30
};
console.log(person); // Output: { name: "John", age: 30 }
person.name = "Jane";
console.log(person); // Output: { name: "Jane", age: 30 }
person = {name: "jim", age: 40} // This will throw an error because person is a constant and cannot be reassigned
In summary, you should use const when you want to create a variable that you don’t intend to reassign. It helps to protect your code and make it more readable by making it clear that certain values should not be modified.
Creating function with const
When creating a function, it’s generally best practice to use const to declare the function. This is because the function itself is not going to be reassigned to a new value, so it makes sense to use const to indicate that the function cannot be changed.
Here is an example of declaring a function with const:
const add = function(a, b) {
return a + b;
};
console.log(add(1, 2)); // Output: 3
Using const to declare function can also help prevent accidental reassignment, which can lead to bugs in your code. Since the function is a constant, you will get an error if you try to reassign it.
const add = function(a, b) {
return a + b;
};
add = function(a, b, c){ return a+b+c } // This will throw an error because add is a constant and cannot be reassigned
In summary, using const when creating a function is a good practice because it makes it clear that the function should not be reassigned and helps to prevent accidental reassignments that can lead to bugs in your code.