What is tslint?
The tslint npm package is a static analysis tool that checks TypeScript code for readability, maintainability, and functionality errors. It is widely used to enforce a consistent code style by checking the code against a set of linting rules.
What are tslint's main functionalities?
Linting TypeScript Files
This feature allows you to lint TypeScript files by specifying a configuration file and a pattern to match files. The command will process all TypeScript files in the 'src' directory and its subdirectories.
tslint -c tslint.json 'src/**/*.ts'
Fixing Linting Errors Automatically
This feature automatically fixes linting errors that can be corrected without human intervention. It is useful for fixing simple issues like whitespace or semicolon usage.
tslint --fix -c tslint.json 'src/**/*.ts'
Custom Rules
This feature allows you to use custom linting rules in addition to the predefined rules. You can specify a directory containing custom rule definitions to be applied to your code.
tslint -c tslint.json 'src/**/*.ts' --rules-dir custom_rules
Other packages similar to tslint
eslint
ESLint is a popular linting tool for JavaScript and TypeScript. It is highly configurable and extendable, with a large ecosystem of plugins. ESLint has effectively replaced TSLint as the preferred linter for TypeScript after TSLint's deprecation.
prettier
Prettier is an opinionated code formatter that supports many languages, including TypeScript. While it does not perform static code analysis, it formats code to a consistent style. Prettier can be used alongside linters like ESLint.
stylelint
Stylelint is a modern linter that helps you avoid errors and enforce conventions in your stylesheets. Although it is primarily used for CSS, it can be used in conjunction with PostCSS to lint SCSS, Sass, Less, and other CSS-like languages.
TSLint
A linter for the TypeScript language.
Supported Rules
ban
bans the use of specific functions. Options are ["object", "function"] pairs that ban the use of object.function()class-name
enforces PascalCased class and interface names.comment-format
enforces rules for single-line comments. Rule options:
"check-space"
enforces the rule that all single-line comments must begin with a space, as in // comment
- note that comments starting with
///
are also allowed, for things such as ///
"check-lowercase"
enforces the rule that the first non-whitespace character of a comment must be lowercase, if applicable
curly
enforces braces for if
/for
/do
/while
statements.eofline
enforces the file to end with a newline.forin
enforces a for ... in
statement to be filtered with an if
statement.*indent
enforces consistent indentation levels (currently disabled).interface-name
enforces the rule that interface names must begin with a capital 'I'jsdoc-format
enforces basic format rules for jsdoc comments -- comments starting with /**
- each line contains an asterisk and asterisks must be aligned
- each asterisk must be followed by either a space or a newline (except for the first and the last)
- the only characters before the asterisk on each line must be whitepace characters
label-position
enforces labels only on sensible statements.label-undefined
checks that labels are defined before usage.max-line-length
sets the maximum length of a line.no-arg
disallows access to arguments.callee
.no-bitwise
disallows bitwise operators.no-console
disallows access to the specified functions on console
. Rule options are functions to ban on the console variable.no-consecutive-blank-lines
disallows having more than one blank line in a row in a fileno-construct
disallows access to the constructors of String
, Number
, and Boolean
.no-debugger
disallows debugger
statements.no-duplicate-key
disallows duplicate keys in object literals.no-duplicate-variable
disallows duplicate variable declarations.no-empty
disallows empty blocks.no-eval
disallows eval
function invocations.no-string-literal
disallows object access via string literals.no-trailing-comma
disallows trailing comma within object literals.no-trailing-whitespace
disallows trailing whitespace at the end of a line.no-unused-variable
disallows unused imports, variables, functions and private class members.no-unreachable
disallows unreachable code after break
, catch
, throw
, and return
statements.no-use-before-declare
disallows usage of variables before their declaration.one-line
enforces the specified tokens to be on the same line as the expression preceding it. Rule options:
"check-catch"
checks that catch
is on the same line as the closing brace for try
"check-else"
checks that else
is on the same line as the closing brace for if
"check-open-brace"
checks that an open brace falls on the same line as its preceding expression."check-whitespace"
checks preceding whitespace for the specified tokens.
quotemark
enforces consistent single or double quoted string literals.radix
enforces the radix parameter of parseInt
semicolon
enforces semicolons at the end of every statement.triple-equals
enforces === and !== in favor of == and !=.typedef
enforces type definitions to exist. Rule options:
"callSignature"
checks return type of functions"catchClause"
checks type in exception catch blocks"indexSignature"
checks index type specifier of indexers"parameter"
checks type specifier of parameters"propertySignature"
checks return types of interface properties"variableDeclarator"
checks variable declarations
typedef-whitespace
enforces spacing whitespace for type definitions. Each rule option requires a value of "space"
or "nospace"
to require a space or no space before the type specifier's colon. Rule options:
"callSignature"
checks return type of functions"catchClause"
checks type in exception catch blocks"indexSignature"
checks index type specifier of indexers
use-strict
enforces ECMAScript 5's strict mode
check-module
checks that all top-level modules are using strict modecheck-function
checks that all top-level functions are using strict mode
variable-name
allows only camelCased or UPPER_CASED variable names. Rule options:
"allow-leading-underscore"
allows underscores at the beginnning.
whitespace
enforces spacing whitespace. Rule options:
"check-branch"
checks branching statements (if
/else
/for
/while
) are followed by whitespace"check-decl"
checks that variable declarations have whitespace around the equals token"check-operator"
checks for whitespace around operator tokens"check-separator"
checks for whitespace after separator tokens (,
/;
)"check-type"
checks for whitespace before a variable type specification
TSLint Rule Flags
You can enable/disable TSLint or a subset of rules within a file with the following comment rule flags:
/* tslint:disable */
- Disable all rules for the rest of the file/* tslint:enable */
- Enable all rules for the rest of the file/* tslint:disable:rule1 rule2 rule3... */
- Disable the listed rules for the rest of the file/* tslint:enable:rule1 rule2 rule3... */
- Enable the listed rules for the rest of the file
Rules flags enable or disable rules as they are parsed. A rule is enabled or disabled until a later directive commands otherwise. Disabling an already disabled rule or enabling an already enabled rule has no effect.
For example, imagine the directive /* tslint:disable */
on the first line of a file, /* tslint:enable:ban class-name */
on the 10th line and /* tslint:enable */
on the 20th. No rules will be checked between the 1st and 10th lines, only the ban
and class-name
rules will be checked between the 10th and 20th, and all rules will be checked for the remainder of the file.
Installation
CLI
sudo npm install tslint -g
Library
npm install tslint
Usage
Please first ensure that the TypeScript source files compile correctly.
CLI
usage: tslint
Options:
-c, --config configuration file
-f, --file file to lint [required]
-o, --out output file
-r, --rules-dir rules directory
-s, --formatters-dir formatters directory
-t, --format output format (prose, json) [default: "prose"]
By default, configuration is loaded from tslint.json
, if it exists in the current path.
tslint accepts the following commandline options:
-f, --file:
The location of the TypeScript file that you wish to lint. This
option is required.
-c, --config:
The location of the configuration file that tslint will use to
determine which rules are activated and what options to provide
to the rules. If no option is specified, the config file named
tslint.json is used, so long as it exists in the path.
The format of the file is { rules: { /* rules list */ } },
where /* rules list */ is a key: value comma-seperated list of
rulename: rule-options pairs. Rule-options can be either a
boolean true/false value denoting whether the rule is used or not,
or a list [boolean, ...] where the boolean provides the same role
as in the non-list case, and the rest of the list are options passed
to the rule that will determine what it checks for (such as number
of characters for the max-line-length rule, or what functions to ban
for the ban rule).
-o, --out:
A filename to output the results to. By default, tslint outputs to
stdout, which is usually the console where you're running it from.
-r, --rules-dir:
An additional rules directory, for user-created rules.
tslint will always check its default rules directory, in
node_modules/tslint/build/rules, before checking the user-provided
rules directory, so rules in the user-provided rules directory
with the same name as the base rules will not be loaded.
-s, --formatters-dir:
An additional formatters directory, for user-created formatters.
Formatters are files that will format the tslint output, before
writing it to stdout or the file passed in --out. The default
directory, node_modules/tslint/build/formatters, will always be
checked first, so user-created formatters with the same names
as the base formatters will not be loaded.
-t, --format:
The formatter to use to format the results of the linter before
outputting it to stdout or the file passed in --out. The core
formatters are prose (human readable) and json (machine readable),
and prose is the default if this option is not used. Additional
formatters can be added and used if the --formatters-dir option
is set.
--help:
Prints this help message.
Library
var options = {
formatter: "json",
configuration: configuration,
rulesDirectory: "customRules/",
formattersDirectory: "customFormatters/"
};
var Linter = require("tslint");
var ll = new Linter(fileName, contents, options);
var result = ll.lint();
Development
Setup
git clone git@github.com:palantir/tslint.git
Build
npm install
grunt