if (req.url === "/script.js")

If Statement: Explaining "if (req.url === "/script.js")"

In JavaScript, the "if" statement is used to execute a block of code only if a certain condition is true. The condition is usually enclosed in parentheses and followed by the code block wrapped in curly braces. The condition can be a comparison, a variable, a function, or any other expression that evaluates to a Boolean value.

In the given code snippet, the condition is checking if the URL of the current request is equal to "/script.js". It uses the strict equality operator "===" to compare the two values. This means that not only the values have to be the same, but also their types have to match.

      if (req.url === "/script.js") {
        // execute some code here
      }
    

The above code block will only execute if the URL of the current request matches exactly "/script.js". If it doesn't match or if there is no URL specified, the code block will be skipped.

There can be multiple ways to write the same code with different syntax or logic. For example, instead of using strict equality, we can use loose equality "==", which compares the values regardless of their types:

      if (req.url == "/script.js") {
        // execute some code here
      }
    

This will work the same as the previous code block for most cases, but it can have unexpected behavior if the two values have different types that can be coerced into each other. Therefore, it's generally recommended to use strict equality to avoid such bugs.

Another way to write the same code is to use a ternary operator, which is a shorthand for the "if-else" statement:

      (req.url === "/script.js") ? 
      // execute some code here if the condition is true
      :
      // execute some other code here if the condition is false
    

This code will execute the first code block if the condition is true, and the second code block if the condition is false. This can be useful for writing shorter and more concise code, but it can also make the code harder to read and understand if the condition or the code blocks are complex.