What is a side effect?
Side effect occurs in a program whenever you use an external code in your function, which impacts the function’s ability to perform its task.
Example 1: Add an old value to a new one
let oldDigit = 5;function addNumber(newValue) {return oldDigit += newValue;}// 5+5 = 10
In the snippet above, oldDigit’s usage within the function makes addNumber() have the following side effects:
First: Dependency on oldDigit
The fact that addNumber() depends on oldDigit to successfully perform its duties means that whenever oldDigit is addNumber() will return a faulty result.
Second: Modifies an external code
As addNumber() is programmed to mutate oldDigit’s addNumber() has a side effect where it manipulates the external code.
Third: Becomes a non-deterministic function
The use of an external code in addNumber() makes it a
In other words, to be sure of addNumber()’s return value, you must consider other external factors, such as the current state of oldDigit.
Therefore, addNumber() is not independent as it always has strings attached.
Example 2: Print text onto your console
function printName() {console.log("My name is Oluwatobi Sofela.");}
In the snippet above, console.log()’s usage within printName() makes the function have side effects.
How does console.log cause a function to have side effects?
A console.log() causes a function to have side effects because it affects console object’s state
In other words, console.log() instructs the computer to alter the console object’s state.
As such, when you use it within a function, it causes that function to:
-
Be dependent on the
consoleobject to perform its job effectively. -
Modify the state of an external code (that is, the
consoleobject’s state). -
Become non-deterministic, as you must now consider the
console’s state to be sure of the function’s output.
