backend-tslint-rules

v1.14.0

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3 years ago

Shared TSLint rules to enforce a consistent code style for backend development with TypeScript

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linting-rules tslint backend nodejs

backend-tslint-rules

Shared TSLint rules to enforce a consistent code style for backend development with TypeScript

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The value of the software produced is directly affected by the quality of the codebase, and not every developer might

be aware of the potential pitfalls of certain constructions in TypeScript,
know that not every developer is as capable in understanding an elegant (but abstract) solution as the original developer.

For that purpose, we need to use static code analysis tools such as TSLint to check readability, maintainability, and functionality errors.

Although complying with these tools may seem to appear as undesired overhead or may limit creativity, it becomes easier for any new developers to read, preventing a lot of time/frustration spent figuring out the structure and characteristics of the code.

Containing a set of TSLint rules, backend-tslint-rules has been compiled using many contributions from colleagues, commercial/open-source projects and some other sources from the Internet, as well as years of development using the [Angular] framework.

If you have questions, comments or suggestions, just create an issue on this repository. I'll try to revise and republish these rules with new insights, experiences and remarks in alignment with the updates on TSLint.

Note: The following set of rules depend on:

TSLint v5.12.0

Getting started

Installation

You can install backend-tslint-rules using npm

npm install backend-tslint-rules --save

Note: You should have already installed TSLint.

Usage

To use these TSLint rules, use configuration inheritance via the extends keyword.

A sample configuration is shown below, where tslint.json lives adjacent to your node_modules folder:

{
  "extends": ["backend-tslint-rules"],
  "rules": {
    // override tslint rules here
    ...
  }
}

Rules

Class and Member design

Do not use classes unless required.

"no-unnecessary-class": [
  true,
  "allow-constructor-only",
  "allow-static-only",
  "allow-empty-class"
]

Do not specify the public keyword (this is the default accessibility level).
private and private static members in classes should be denoted with the private keyword.

"member-access": [
  true,
  "no-public"
]

Member ordering should be in the following way:
- Public members should be ordered before private members.
- Static members should be ordered before instance members.
- Variables should be ordered before functions.

"member-ordering": [
  true,
  "public-before-private",
  "static-before-instance",
  "variables-before-functions"
]

Always prefer readonly private members (maintain immutability).

"prefer-readonly": true

Member overloads should be consecutive.

"adjacent-overload-signatures": true

Always prefer unifying any two overloads into one, by using a union or an optional/rest parameter.

"unified-signatures": true

Always prefer functions over private members that do not use this.

"prefer-function-over-method": [
  true,
  "allow-public",
  "allow-protected"
]

Do not use a class method outside of a method call.

"no-unbound-method": [true, "ignore-static"]

Do not use the this keyword outside class context (including functions in methods).

"no-invalid-this": [
  true,
  "check-function-in-method"
]

Do not use this in static methods.

"static-this": true

Do not assign this to local variables.

"no-this-assignment": true

Do not use blank constructors.

"unnecessary-constructor": true

Do not invoke the super method twice in a constructor (except in branched statements or nested class constructors).

"no-duplicate-super": true

Always prefer parentheses () when invoking a constructor via the new keyword.

"new-parens": true

Do not define new for classes.

"no-misused-new": true

Do not use the constructors of String, Number, and Boolean.

"no-construct": true

Interface design

Do not define constructors for interfaces.

See: Class and Member design

Do not use empty interfaces.

"no-empty-interface": true

Always prefer foo(): void over foo: () => void in interfaces and types.

"prefer-method-signature": true

Always prefer an interface declaration over a type literal (type T = { ... }).

"interface-over-type-literal": true

Function design

Functions should be defined right after the variable declarations.

See: Class and Member design

Do not use the built-in function constructor.

"function-constructor": true

Do not reassign function parameters (maintain immutability).

"no-parameter-reassignment": true

Do not use void expressions in statement position.

"no-void-expression": true

Always prefer return; in void functions and return undefined; in value-returning functions.

"return-undefined": true

Do not invoke arguments.callee within a function, as it makes impossible various performance optimizations.

"no-arg": true

Anonymous functions

Always prefer defining anonymous functions as fat-arrow/lambda () => { } functions.

"only-arrow-functions": true

fat-arrow/lambda functions should have parenthesis () around the function parameters (except if removing them is allowed by TypeScript).

"arrow-parens": [
  true,
  "ban-single-arg-parens"
]

Always prefer () => x over () => { return x; }.

"arrow-return-shorthand": [
  true,
  "multiline"
]

Always prefer just f over x => f(x).

"no-unnecessary-callback-wrapper": true

Do not use unnecessary and/or misleading scope bindings on functions.

"unnecessary-bind": true

Async functions

Always prefer marking async functions returning a Promise.

"promise-function-async": true

Do not use the unnecessary async (if the awaited value that is not a Promise).

"await-promise": true

Do not use the unnecessary return await.

"no-return-await": true

Do not use floating Promise.

"no-floating-promises": true

Variable design

Do not use a variable before declaring.

"no-use-before-declare": true

Always prefer const keyword where appropriate, for values that should never change.
Avoid using let (maintain immutability).

"prefer-const": true

Do not use the var keyword.

"no-var-keyword": true

Do not use implied global variables.
Do not define a variable on the global scope from within a smaller scope.

"no-shadowed-variable": [
  true,
  {
    "temporalDeadZone": false
  }
]

Declare one variable at a time (except in loops).

"one-variable-per-declaration": [
  true,
  "ignore-for-loop"
]

Do not use duplicate variable names in the same block scope.

"no-duplicate-variable": [
  true,
  "check-parameters"
]

Do not use a var/let statement or destructuring initializer to be initialized to undefined.

"no-unnecessary-initializer": true

Requires and Imports

Do not import modules that are not listed as a dependency in the project's package.json.

"no-implicit-dependencies": true

Do not use import statements with side-effect.

"no-import-side-effect": true

Always use the import statement keywords in alphabetical order.

"ordered-imports": [
  true,
  {
    "import-sources-order": "case-insensitive",
    "named-imports-order": "case-insensitive",
    "grouped-imports": false
  }
]

Always use a single import statement per module.

"no-duplicate-imports": true

Do not use require statements at all (use ES6-style import statement instead).

"no-require-imports": true

Do not use default imports and exports in ES6-style modules.

"no-default-import": true,
"no-default-export": true

Do not use /// <reference path=> imports statements at all (use ES6-style import statement instead).

"no-reference": true

Types

Always prefer defining the return type of functions, methods and property declarations explicitly.
Types should be used whenever necessary (no implicit any).

"typedef": [
  true,
  "call-signature",
  "property-declaration"
]

Always prefer type inference over explicit type declaration (except for function return types).

"no-inferrable-types": true

Do not use the default type arguments explicitly.

"use-default-type-parameter": true

Meanwhile, avoid type assertion for object literals.

"no-object-literal-type-assertion": true

Always prefer the use of as Type for type assertions over <Type>.

"no-angle-bracket-type-assertion": true

Do not use unnecessary type assertions.

"no-unnecessary-type-assertion": true

Always prefer writing an interface or literal type with just a call signature as a function type.

"callable-types": true

Do not use the null keyword, always return undefined instead of a null reference.

"no-null-keyword": true

Do not use non-null assertions.

"no-non-null-assertion": true

Arrays should be defined as Array<type> instead of type[].

"array-type": [
  true,
  "generic"
]

Objects

Always prefer ES6 object spread operator whenever possible.

"prefer-object-spread": true

Always prefer ES6 object literal shorthand whenever possible.

"object-literal-shorthand": true

Always prefer object property names using literals whenever possible.

"object-literal-key-quotes": [
  true,
  "as-needed"
]

Do not use string literal property access.

"no-string-literal": true

Strings

Always prefer single-quotes '' for all strings, and use double-quotes "" for strings within strings.

"quotemark": [
  true,
  "single",
  "avoid-template",
  "avoid-escape"
]

Always prefer template expressions over string literal concatenation.

"prefer-template": true

Do not use string templates outside template strings (``).

"no-invalid-template-strings": true

Operators

Always prefer using === and !== operators whenever possible.

== and != operators do type coercion, which can lead to headaches when debugging code.

"triple-equals": [
  true,
  "allow-null-check"
]

Always prefer explicit += 1 and -= 1 pre-unary operators over ++i and --i.

"increment-decrement": [
  true,
  "allow-post"
]

Always prefer using operands of the same type with the `+`` operator.

"restrict-plus-operands": true

In a binary expression, a literal should always be on the right-hand side.

"binary-expression-operand-order": true

Do not use the delete operator with dynamic key expressions.

"no-dynamic-delete": true

Always prefer using isNan function to check NaN references.

"use-isnan": true

Assignment expressions inside of the condition block of if, while, and do while statements should be avoided.

"no-conditional-assignment": true

Conditional statements

Always prefer conditional expression over a standard if statement.

"prefer-conditional-expression": [
  true,
  "check-else-if"
]

Do not compare to two equal variables/literals as operands (ex: 3 === 3, someVar === someVar).

"no-tautology-expression": true

Do not compare to a boolean literal (ex: x === true).

"no-boolean-literal-compare": true

Do not use else blocks ending with a break, continue, return or throw statement.

"unnecessary-else": true

Do not use any always truthy/falsy condition in boolean expressions (except right-hand operand && or ||).

"strict-boolean-expressions": [
  true,
  "allow-undefined-union",
  "allow-string",
  "allow-enum",
  "allow-number",
  "allow-mix",
  "allow-rhs"
]

`for` statement

Always prefer while loop over a standard for loop without initializer, incrementor and/or termination condition.

"prefer-while": true

Always prefer for-of loop over a standard for loop.

"prefer-for-of": true

Filter for-in statements with an if statement (this prevents accidental iteration over properties inherited from an object???s prototype).

"forin": true

Do not iterate over an array with a for-in loop.

"no-for-in-array": true

`switch` statement

Each switch statement should have a default case.

"switch-default": true

Each switch case except default should end with break, return, or throw.

"no-switch-case-fall-through": true

Do not use duplicate switch cases.

"no-duplicate-switch-case": true

`try` statement

Do not use control flow statements, such as return, continue, break and throws in finally blocks.

"no-unsafe-finally": true

Maintainability

Use UTF-8 encoding.

"encoding": true

Limit the level of complexity (cyclomatic complexity) in a function/method by 20 branches.

"cyclomatic-complexity": [
  true,
  20
]

Files should not exceed 1500 lines of code.

"max-file-line-count": [true, 1500]

Keep the length of each line under 140 characters.

"max-line-length": [
  true,
  140
]

Use 2 spaces for indentation.

"indent": [
  true,
  "spaces",
  2
]

All files should end in a new line.

"eofline": true

Layout

Curly braces

Always Use curly braces.

"curly": true

Whitespace

Whitespaces should be used in the following circumstances:

All branching statements (if/else/for/while) should be followed by one space.
Variable declarations should be separated by one space around the type specification and equals token.
There should be one space between the typecast and its target.
All operators except the period ., left parenthesis (, and left bracket [ should be separated from their operands by one space.
There should be no space between the unary/incremental operators !x, -x, +x, ~x, ++x, --x and its operand.
There should be one space between the type operators |, & and its operand.
There should be one space after the left curly brace { and before the right curly brace } containing import statement keywords.
Each separator (,,;) in the control part of a for statement should be followed with one space.
There should be no space after the rest/spread operator ....
The left curly brace { followed by a right parenthesis ) should always separated by one space.

"whitespace": [
  true,
  "check-branch",
  "check-decl",
  "check-operator",
  "check-module",
  "check-separator",
  "check-rest-spread",
  "check-type",
  "check-typecast",
  "check-type-operator",
  "check-preblock"
]

For each call signature, index signature, parameter, property declaration and variable declaration;
- There should be no space between the parameter and the colon : indicating the type declaration.
- There should be one space between the colon : and the type declaration.

"typedef-whitespace": [
  true,
  {
    "call-signature": "nospace",
    "index-signature": "nospace",
    "parameter": "nospace",
    "property-declaration": "nospace",
    "variable-declaration": "nospace"
  },
  {
    "call-signature": "onespace",
    "index-signature": "onespace",
    "parameter": "onespace",
    "property-declaration": "onespace",
    "variable-declaration": "onespace"
  }
]

For each function, class member and constructor;
- There should be no space between the name of the function/member and the left parenthesis ( of its parameter list.
For each fat-arrow/lambda function;
- There should be one space between the right parenthesis ) and the =>.

"space-before-function-paren": [
  true,
  {
    "anonymous": "never",
    "named": "never",
    "asyncArrow": "always",
    "method": "never",
    "constructor": "never"
  }
]

There should be no space within parenthesis.

"space-within-parens": 0

Put one space between the import statement keywords.

"import-spacing": true

Do not use trailing whitespaces at the end of a line

"no-trailing-whitespace": true

Empty lines

Empty lines improve code readability by allowing the developer to logically group code blocks.

There should be an empty line before the return statement.

"newline-before-return": true

There should be a separate line for each chained method call.

"newline-per-chained-call": true

For each function, anonymous function, class member, constructor, else, catch and finally statements;
- There should be one space between the right parenthesis ) and the left curly { brace that begins the statement body.
For each fat-arrow/lambda function;
- There should be one space between the => and the left curly brace { that begins the statement body.
else statements should indented to align with the line containing the closing brace for the if statement.
catch and finally statements should indented to align with the line containing the closing brace for the try statement.

"one-line": [
  true,
  "check-open-brace",
  "check-whitespace",
  "check-else",
  "check-catch",
  "check-finally"
]

Do not use more than one empty line in a row.

"no-consecutive-blank-lines": [
  true,
  1
]

Alignment

A semicolon should be placed at the end of every simple statement (except at the end of bound class methods).

"semicolon": [
  true,
  "always",
  "strict-bound-class-methods"
]

Vertically align elements, members, parameters and statements (helps maintain a readable, consistent style in your codebase).

"align": [
  true,
  "elements",
  "members",
  "parameters",
  "statements"
]

Do not use trailing commas in array and object literals, destructuring assignments, function typings, named imports/exports and function parameters.

"trailing-comma": [
  true,
  {
    "multiline": "never",
    "singleline": "never",
    "esSpecCompliant": true
  }
]

Naming

Files

Files should be in kebab-case.

"file-name-casing": [
  true,
  "kebab-case"
]

Classes and Interfaces

Class and interface names should be in PascalCase.

"class-name": true

Interface names should not have an I prefix.

"interface-name": [
  true,
  "never-prefix"
]

Variables and Functions

All variable, and function names should be in camelCase.
All variables with UPPER_CASE names must be const.
Do not use trailing underscore _ characters.

"variable-name": [
  true,
  "check-format",
  "allow-leading-underscore",
  "require-const-for-all-caps",
  "ban-keywords"
]

Documentation

Always prefer single-line or JSDoc comments.

"comment-type": [
  true,
  "singleline",
  "doc"
]

Inline Comments

Always prefer // for all inline comments.
There should be one space before the comment.

"comment-format": [
  true,
  "check-space"
]

JSDoc Comments

JSDoc comments should start with /** and end with */.

"jsdoc-format": [
  true,
  "check-multiline-start"
]

Do not use redundant JSDoc comments.

"no-redundant-jsdoc": true

Do not use the // @ts-ignore comments.

"ban-ts-ignore": true

Misc

Do not use the console method (such messages are considered to be for debugging purposes and therefore might ship to the production environment).

"no-console": [
  true,
  "log",
  "debug",
  "info",
  "time",
  "timeEnd",
  "trace"
]

Do not use the debugger statement (this might cause the environment to stop execution and start up a debugger, if not omitted on the production code).

"no-debugger": true

Do not use the eval function (using eval on untrusted code might open a program up to several different injection attacks).

"no-eval": true

Do not throw plain strings or concatenations of strings (because only Errors produce proper stack traces).

"no-string-throw": true

Do not use namespaces (using namespace {} is outdated).

"no-namespace": true

Do not use internal modules (using module {} is outdated).

"no-internal-module": true

Always prefer decimal literals beginning with 0 (instead of .).
Avoid decimal literals ending with a trailing 0.

"number-literal-format": true

Always prefer the radix parameter to be specified when calling parseInt.

"radix": true

Do not leave unused expressions in the code.

"no-unused-expression": [
  true,
  "allow-fast-null-checks"
]

Do not use empty blocks {} in the code.

"no-empty": true

Do not use missing elements in arrays.

"no-sparse-arrays": true

Do not use comma operator.

"ban-comma-operator": true

Contributing

If you want to file a bug, contribute some code, or improve documentation, please read up on the following contribution guidelines:

Thanks to

JetBrains, for their support to this open source project with free WebStorm licenses.

License

The MIT License (MIT)

Published

Vulnerabilities

Links

Maintainers

Keywords

Readme

backend-tslint-rules

Table of contents:

Getting started

Installation

Usage

Rules

Class and Member design

Interface design

Function design

Anonymous functions

Async functions

Variable design

Requires and Imports

Types

Objects

Strings

Operators

Conditional statements

for statement

switch statement

try statement

Maintainability

Layout

Curly braces

Whitespace

Empty lines

Alignment

Naming

Files

Classes and Interfaces

Variables and Functions

Documentation

Inline Comments

JSDoc Comments

Misc

Contributing

Thanks to

License

`for` statement

`switch` statement

`try` statement