typescript.md

TypeScript coding guide

TypeScript is a superset of JavaScript that greatly helps building large web applications.

Coding conventions and best practices comes from the TypeScript guidelines, and are also detailed in the TypeScript Deep Dive Style Guide. In addition, this project also follows the general Angular style guide.

Naming conventions

• Use PascalCase for types, classes, interfaces, constants and enum values.
• Use camelCase for variables, properties and functions
• Avoid prefixing interfaces with a capital I, see Angular style guide
• Do not use _ as a prefix for private properties. An exception can be made for backing fields like this:

  private _foo: string;
  get foo() { return this._foo; } // foo is read-only to consumers

Ordering

• Within a file, type definitions should come first
• Within a class, these priorities should be respected:
  • Properties comes before functions
  • Static symbols comes before instance symbols
  • Public symbols comes before private symbols

Coding rules

• Use single quotes ' for strings
• Always use strict equality checks: === and !== instead of == or != to avoid comparison pitfalls (see JavaScript equality table). The only accepted usage for == is when you want to check a value against null or undefined.
• Use [] instead of Array constructor
• Use {} instead of Object constructor
• Always specify types for function parameters and returns (if applicable)
• Do not export types/functions unless you need to share it across multiple components
• Do not introduce new types/values to the global namespace
• Use arrow functions over anonymous function expressions
• Only surround arrow function parameters when necessary. For example, (x) => x + x is wrong but the following are correct:
  • x => x + x
  • (x, y) => x + y
  • <T>(x: T, y: T) => x === y

Definitions

In order to infer types from JavaScript modules, TypeScript language supports external type definitions. They are located in the node_modules/@types folder.

To manage type definitions, use standard npm install|update|remove commands.

Enforcement

Coding rules are enforced in this project via TSLint. Angular-specific rules are also enforced via the Codelyzer rule extensions.

Learn more

The read of TypeScript Deep Dive is recommended, this is a very good reference book for TypeScript (and also open-source).