tslint.yaml

defaultSeverity: error
rules:
  # -- Strict errors --
  # These lint rules are likely always a good idea.

  # Force function overloads to be declared together. This ensures readers understand APIs.
  adjacent-overload-signatures: true

  # Do not allow the subtle/obscure comma operator.
  ban-comma-operator: true

  # Do not allow internal modules or namespaces . These are deprecated in favor of ES6 modules.
  no-namespace: true

  # Do not allow parameters to be reassigned. To avoid bugs, developers should instead assign new values to new vars.
  no-parameter-reassignment: true

  # Force the use of ES6-style imports instead of /// <reference path=> imports.
  no-reference: true

  # Do not allow type assertions that do nothing. This is a big warning that the developer may not understand the
  # code currently being edited (they may be incorrectly handling a different type case that does not exist).
  no-unnecessary-type-assertion: true

  # Disallow nonsensical label usage.
  label-position: true

  # Disallows the (often typo) syntax if (var1 = var2). Replace with if (var2) { var1 = var2 }.
  no-conditional-assignment: true

  # Disallows constructors for primitive types (e.g. new Number('123'), though Number('123') is still allowed).
  no-construct: true

  # Do not allow super() to be called twice in a constructor.
  no-duplicate-super: true

  # Do not allow the same case to appear more than once in a switch block.
  no-duplicate-switch-case: true

  # Do not allow a variable to be declared more than once in the same block. Consider function parameters in this
  # rule.
  no-duplicate-variable: [true, 'check-parameters']

  # Disallows a variable definition in an inner scope from shadowing a variable in an outer scope. Developers should
  # instead use a separate variable name.
  no-shadowed-variable: true

  # Empty blocks are almost never needed. Allow the one general exception: empty catch blocks.
  no-empty: [true, 'allow-empty-catch']

  # Functions must either be handled directly (e.g. with a catch() handler) or returned to another function.
  # This is a major source of errors in Cloud Functions and the team strongly recommends leaving this rule on.
  no-floating-promises: true

  # Do not allow any imports for modules that are not in package.json. These will almost certainly fail when
  # deployed.
  no-implicit-dependencies:
    - true
    - 'dev'
    - ['~']

  # The 'this' keyword can only be used inside of classes.
  no-invalid-this: true

  # Do not allow strings to be thrown because they will not include stack traces. Throw Errors instead.
  no-string-throw: true

  # Disallow control flow statements, such as return, continue, break, and throw in finally blocks.
  no-unsafe-finally: true

  # Expressions must always return a value. Avoids common errors like const myValue = functionReturningVoid();
  no-void-expression: [true, 'ignore-arrow-function-shorthand']

  # Disallow duplicate imports in the same file.
  no-duplicate-imports: true

  no-unused-variable: true

  # -- Strong Warnings --
  # These rules should almost never be needed, but may be included due to legacy code.
  # They are left as a warning to avoid frustration with blocked deploys when the developer
  # understand the warning and wants to deploy anyway.

  # Warn when an empty interface is defined. These are generally not useful.
  no-empty-interface:
    severity: warning

  # Warn when variables are defined with var. Var has subtle meaning that can lead to bugs. Strongly prefer const for
  # most values and let for values that will change.
  no-var-keyword:
    severity: warning

  # Prefer === and !== over == and !=. The latter operators support overloads that are often accidental.
  triple-equals:
    severity: warning

  # Warn when using deprecated APIs.
  deprecation:
    severity: warning

  # -- Light Warnings --
  # These rules are intended to help developers use better style. Simpler code has fewer bugs. These would be "info"
  # if TSLint supported such a level.

  # prefer for( ... of ... ) to an index loop when the index is only used to fetch an object from an array.
  # (Even better: check out utils like .map if transforming an array!)
  prefer-for-of:
    severity: warning

  # Warns if function overloads could be unified into a single function with optional or rest parameters.
  unified-signatures:
    severity: warning

  # Prefer const for values that will not change. This better documents code.
  prefer-const:
    severity: warning

  # Multi-line object literals and function calls should have a trailing comma. This helps avoid merge conflicts.
  trailing-comma:
    severity: warning