Functions

As your Pine Script indicators grow, you will start noticing repeated patterns in your code. The same RSI calculation used three times. The same support/resistance logic copied across scripts. The same color-selection block appearing everywhere. Functions solve this by letting you write a piece of logic once and reuse it wherever you need it.

This tutorial covers both Pine Script's extensive library of built-in functions and how to create your own. By the end, you will build a complete custom indicator composed of small, focused functions.

Why Functions Matter

Functions provide three benefits that become critical as your scripts grow:

1. DRY (Don't Repeat Yourself): Write the logic once, call it many times. If you need to change it, you change it in one place.
2. Readability: isStrongBullish(close, volume) communicates intent far better than five lines of raw conditions.
3. Testability: Small, isolated functions are easier to verify and debug than monolithic scripts.

Built-in Functions: The ta Library

Pine Script's ta namespace contains dozens of pre-built technical analysis functions. These are optimized internally and handle edge cases (like insufficient data on early bars) for you. Let's explore the most important ones with trading context.