> For the complete documentation index, see [llms.txt](https://docs.elentra.org/ejs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.elentra.org/ejs/1.0/guide/introduction/standards-and-principles.md).

# Standards & Principles

## Definitions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC 2119](https://tools.ietf.org/html/rfc2119) and updated by [RFC 8174](https://tools.ietf.org/html/rfc8174).

## Code Standards <a href="#code-standards" id="code-standards"></a>

* All code MUST be written in American English (i.e. variable/method/class names, etc).
* ES6 / ECMA2015 MUST be used in [strict mode](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode).
* Classes MUST be defined with ES6 class syntax.
* Each class MUST be declared in its own file.
* Code MUST NOT be placed outside of a class or VueJS component definition.
* Code MUST NOT be placed in the global namespace.
* A semicolon (;) is REQUIRED at the end of all expressions (including VueJS component definitions).
* Abbreviations in class/method/function names MUST NOT be all uppercase.
* Good: MyJsonMethod
* Bad: \~\~MyJSONMethod\~\~
* All variables MUST be declared on their own line.
* Custom tag names defined by a VueJS component MUST adhere to the [W3C rules](https://www.w3.org/TR/custom-elements/) (all-lowercase, must include a hyphen).
* Code block length MUST be limited for readability, reusability, and focused reasoning:
* Classes SHOULD NOT exceed 300 lines and MUST NOT exceed 500 lines.
* Functions/methods SHOULD NOT exceed 50 lines and MUST NOT exceed 150 lines.

## On Dependencies

* External dependencies SHOULD only be used when absolutely necessary. Instead, prefer a stable and unified codebase.
* All external dependencies MUST be wrapped in an interface class to limit coupling to a single location in the code base.
* An external dependency MUST NOT be used directly in application code.
* For example, use the ElentraJS/Http/RestClient instead of Fetch API or Axios directly. This allows us to swap out either library with zero refactoring of the code base.
* Web APIs that are not yet fully standardized MUST be wrapped in an interface class to enable easy updates if the spec changes.

## Design Principles <a href="#design-principles" id="design-principles"></a>

* Favor [composition over inheritance](https://en.wikipedia.org/wiki/Composition_over_inheritance)
* Use [SOLID design](https://en.wikipedia.org/wiki/SOLID_\(object-oriented_design\))
* Aim for [DRY code](https://en.wikipedia.org/wiki/Don%27t_repeat_yourself), but not at the expense of SOLID design.
* Design for accessibility from the start
* Security by default
* First-class localization support
* Reference [Eloquent JavaScript](http://eloquentjavascript.net/)