How can you declare a constant variable in JavaScript?
To declare a constant variable in JavaScript, you can use the `const` keyword. The `const` keyword is used to define a variable that cannot be reassigned or redeclared once it has been initialized. This means that the value of a constant variable remains the same throughout the program.
To declare a constant variable, you need to follow the syntax:
javascript const variableName = value;
Here, `variableName` is the name you want to give to your constant variable, and `value` is the initial value you want to assign to it. It is important to note that you must initialize a constant variable at the time of declaration. If you try to declare a constant variable without assigning an initial value, it will result in a syntax error.
For example, let's declare a constant variable `PI` and assign the value of 3.14159 to it:
javascript const PI = 3.14159;
Once a constant variable has been declared and initialized, you cannot modify its value. If you try to reassign a value to a constant variable, it will generate an error. For instance, the following code will result in a TypeError:
javascript const PI = 3.14159; PI = 3.14; // Error: Assignment to constant variable.
Constants are particularly useful when you want to define values that should not be changed, such as mathematical constants or configuration values. By using constants, you can ensure that these values remain consistent and prevent accidental modifications.
It is important to understand that while the value of a constant variable cannot be changed, it does not mean that the value itself is immutable. For example, if you declare a constant variable with an object as its value, you can still modify the properties of that object. The immutability only applies to the reference of the constant variable, not the value it holds.
javascript
const person = {
name: "John",
age: 30
};
person.age = 31; // Valid, modifies the property of the object
person = {}; // Error: Assignment to constant variable.
To declare a constant variable in JavaScript, you can use the `const` keyword followed by the variable name and its initial value. Once declared, the value of a constant variable cannot be changed or reassigned. Constants are useful for defining values that should remain constant throughout the program.
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