Is console.log inside a function a side effect?

Yes, console.log inside a function is a side effect because it changes the external environment — it outputs data to the console, which affects the outside world of the program.

A side effect is any action of a function that goes beyond returning a value, for example:

• modifying global variables
• input/output (logging, network operations, file system)
• changing UI state

Example:

function greet(name) {
  console.log(`Hello, ${name}!`); // side effect
  return `Hello, ${name}!`;
}

Here, console.log is a side effect, and the returned value is a pure result.