How do you declare Constant in JavaScript ?
In JavaScript, you can declare constants using the const keyword. Constants are variables whose values cannot be re-assigned once they are defined. Here's the syntax to declare a constant in JavaScript:
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const constantName = value;
Here's an example:
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const PI = 3.14159;
console.log(PI); // Output: 3.14159
// Trying to re-assign a value to a constant will result in an error
PI = 3.14; // Error: Assignment to constant variable
In the example above, PI is declared as a constant with the value of 3.14159. Any attempt to re-assign a value to PI will throw an error because it is a constant.
It's important to note that the scope of a constant is block-level. This means that a constant is only accessible within the block where it is defined or within nested blocks. For example:
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function example() {
const x = 10;
if (true) {
const y = 20;
console.log(x); // Output: 10
console.log(y); // Output: 20
}
console.log(x); // Output: 10
console.log(y); // Error: y is not defined
}
In the example above, the constant x is accessible both within the example function and the if block. However, the constant y is only accessible within the if block. Attempting to access y outside of the if block will result in an error.
By convention, constant names are usually written in uppercase to indicate that their values should not be changed, but this is not a strict requirement in JavaScript.
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