Pure function

Pure functions are functions that:

• Return values depend solely on their arguments
• Return the same result when using the same arguments
• No side effects such as database call (insert into database)
• Do not modify arguments that are passed in to maintain immutability

Example:

//x and y are not being modified
//no side effects since always returns sum of x and y
function add(x, y){
    return x + y;
}

On the other hand, Impure functions are functions that:

• Have side effects such as database or network call which might alter the results everytime the function is executed
• Modify arguments that are passed in

Example:

//items have been modified inside the function
function appendTest(items){
    for(let i = 0; i < items.length; i++>){
        items[i] = items[i] + "Test";
    }
}