Introduction to CoffeeLint

CoffeeLint is a static code analysis tool for CoffeeScript. It helps developers identify and fix issues in their CoffeeScript code, following best practices and coding standards. By integrating CoffeeLint into your development workflow, you can improve code quality and maintainability.

Getting Started with CoffeeLint

To start using CoffeeLint, you’ll need to install it via npm:

npm install -g coffeelint

Configuration File

CoffeeLint uses a configuration file named coffeelint.json to specify rules. Here is an example configuration file:

{
  "no_trailing_semicolons": {
    "level": "error"
  },
  "max_line_length": {
    "value": 100,
    "level": "warn"
  }
}

Running CoffeeLint

To lint a CoffeeScript file, use:

coffeelint yourfile.coffee

To lint multiple files, provide a glob pattern:

coffeelint src/**/*.coffee

Commonly Used Rules

• no_trailing_whitespace: Ensures there is no trailing whitespace.
• indentation: Enforces consistent indentation levels (default: 2 spaces).
• camel_case_classes: Enforces class names to be in camel case.
• no_throwing_strings: Disallows throwing string literals as exceptions.

Custom Rules

You can also create custom rules for CoffeeLint. Here’s an example of a simple custom rule:

// my_custom_rule.js
module.exports = {
  name: "no_debugger",
  tokens: [ 'IDENTIFIER' ],
  lintToken: function(token, tokenApi) {
    if (token[1] === 'debugger') {
      return {
        context: 'Unexpected use of debugger.',
        lineNumber: token[2],
      };
    }
  }
};

To add this custom rule to CoffeeLint, include it in your configuration file:

{
  "no_debugger": {
    "module": "./path/to/my_custom_rule.js",
    "level": "error"
  }
}

Example Application

Here’s an example of a simple CoffeeScript application and how to lint it with CoffeeLint:

Application Code

# app.coffee
class Greeter
  constructor: (@name) ->
  greet: ->
    console.log "Hello, #{@name}!"

greeter = new Greeter("World")
greeter.greet()

Linting the Application

First, set up a coffeelint.json for the project:

{
  "no_trailing_semicolons": {
    "level": "error"
  },
  "camel_case_classes": {
    "level": "error"
  },
  "no_debugger": {
    "module": "./path/to/my_custom_rule.js",
    "level": "error"
  }
}

Now, run CoffeeLint:

coffeelint app.coffee

Your output should highlight any linting errors based on the configured rules. By addressing these issues, you ensure that your code adheres to coding standards and is free of common errors.

CoffeeLint is a powerful tool for maintaining high standards in your CoffeeScript projects. With the right configuration, it can help you catch errors early and ensure a consistent codebase.

Happy coding!

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