How to Troubleshoot JavaScript Code in Displayr

Introduction

This article describes useful methods for troubleshooting custom JavaScript code.

A JavaScript variable, Rule or QScript.

You can improve readability by formatting your code as follows:

Write lots of comments to document what your JavaScript is meant to do. A comment starts with //. This is a great help if you are trying to figure out your script months later, or if someone else is reading your script.
```
// Comments are ignored by JavaScript, but are a great help to you.
```
Use the Tab key on your keyboard to make your code more readable. Whenever you write an if/else/for line, use Tab on the next line.
```
if (result < 10) { 
    if (result < 5) 
        result = 5; 
    else 
        result = 10; 
}
```

When writing JavaScript code, you need to be exact and pay attention to:

The presence or absence of semi-colons: they signal that you’re ready for the next bit of the expression.
The capitalization of letters: case-sensitivity means that dog does not equal Dog or DOG.
The right number of brackets (and where they open/close).
Whether brackets are (round) or {curly} or [square].
When symbols are doubled: double ampersands (&&) for “AND”, double-equal signs (==) for equality, and double pipes (||) for "OR".
Index values: JavaScript is 0-based so the first iteration in a loop or array is 0, not 1.
Missing values with your input variables: they can lead to missing results if not handled correctly. For example, if you are summing a set of variables (e.g. q1 + q2 + q3) and one of them returns a NaN (Not a number) for a particular record, the result for that record will also be NaN unless you explicitly address this using the isNaN function or if statements.