The error() Function

Part of the Logic & Flow section of Coddy's Lua journey — lesson 32 of 54.

Sometimes your code needs to stop immediately when something goes wrong. Lua provides the error() function to handle these situations by raising an error and halting script execution.

The error() function takes a message as its argument and stops the program, displaying that message to indicate what went wrong. Here's the basic syntax:

error("Something went wrong!")

This is particularly useful when validating function inputs. For example, if a function expects a positive number but receives a negative one, you can use error() to prevent further execution:

function calculateSquareRoot(num)
    if num < 0 then
        error("Cannot calculate square root of a negative number")
    end
    return math.sqrt(num)
end

When error() is called, the program stops immediately at that point and displays your custom error message. This helps you catch problems early and communicate clearly what went wrong, making your code more reliable and easier to debug.

Cheat sheet

The error() function stops program execution and displays an error message:

error("Something went wrong!")

Common use case - validating function inputs:

function calculateSquareRoot(num)
    if num < 0 then
        error("Cannot calculate square root of a negative number")
    end
    return math.sqrt(num)
end

When error() is called, the program halts immediately and displays the custom error message.

Try it yourself

This lesson doesn't include a code challenge.