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ESLint rules using Regular Expressions

Quick Start

1 . Add dependencies:

package.json:

2 . Configure eslint:

Short configuration:

.eslintrc.json:

Files will be checked for the absence of invalidRegex1 and invalidRegexN, and for the presence of requiredRegex1 and requiredRegexN, and files with name matching ignoreFilesRegex will not be checked.

Detailed configuration:

.eslintrc.json:

Files will be checked for:

• The absence of invalidRegex1 but if found it will be replaced with newValue. • The absence of invalidRegexN only in files with name not matching ignoreFilesRegexN, but if found errorMessageN will be shown. • The presence of requiredRegex1 only in files with name matching inspectFilesRegex1, but if not found errorMessage1 will be shown. • The presence of requiredRegexN only in files with name matching inspectFilesRegexA and not matching ignoreFilesRegexZ.

Goals

The idea is to allow the creation of different eslint rules based on Regular Expressions in order to have some "freedom" to create quick ESLint custom rules.

Rules

Name | Fixable | Description

regex/invalid | Yes | checks that specified patterns are not found regex/required | No | checks that specified patterns are found

Each rule defines a set of patterns:

📏 regex/invalid

This rule checks that specified patterns are not found in files, i.e. Invalid patterns.

✏ Example of incorrect code for this rule:

The error message will reflect the exact location, e.g.:

✏ Example of correct code for this rule:

📏 regex/required

This rule looks for specific patterns that must be present in each file, i.e. Required patterns.

✏ Example of incorrect code for this rule:

The error message will point to the beginning of the file, e.g.:

✏ Example of correct code for this rule:

Options

Both rule has two options:

• array of patterns definitions to analyze. [REQUIRED] • Each pattern definition can be 'Short' or 'Detailed'. • a string representing the regular expression for ignoring files for all patterns. [OPTIONAL]

The *string* representing the regular expression

Remember, Slashes (/) are not required in the string that defines the regex,

e.g. To get the following regex /^(test|spec)$/, define:

• "^(test|spec)$", when using .eslintrc.js or .eslintrc.json.

e.g. To get the following regex /\bhttp:/, define:

• "\bhttp:", when using .eslintrc.js, or • "\\bhttp:", when using .eslintrc.json. (backslash needs to be double in a json file)

e.g. To get the following regex /.*test\.js/, define:

• ".*test\.js", when using .eslintrc.js, or • ".*test\\.js", when using .eslintrc.json. (backslash needs to be double in a json file)

Short pattern definition

Each pattern is specified by just a string representing the regular expression, i.e. "regex"

Detailed pattern definition

It is specified by an object, with the following fields:

• regex: A required string for regex/required and regex/invalid representing the Regular expression to look for. [REQUIRED] • flags: A combination of flags, i, s and/or u, to be used by the Regular Expression. [OPTIONAL] • replacement for regex/invalid [1]: [OPTIONAL] • An optional string used to replace the invalid found pattern, or • An optional object that establish how the invalid found pattern will be replaced: • function: used to replace the invalid found pattern. • It will receive 3 parameters: text, captured and $, that can be used as desired. • It must return a string value, if not, return value will be ignored. • Its definition must be only the body of the function. • One must be defined, either the string or function. • id: An optional string representing the Pattern Id. [OPTIONAL] • message: An optional string specifying the Message to be shown when an error happens (invalid regex is found or required regex is not found). [OPTIONAL] • files: An optional object specifying which files to analyze: [OPTIONAL] • ignore: A string representing Regular expression of the files to be ignored when validating this specific pattern. • inspect: A string representing Regular expression of the files to be inspected when validating this specific pattern.

* regex is the only Required field. * When ignore and inspect are present, ignore takes precedence. * Global ignore file pattern, takes precedence over files patterns.

[1] In order to fix issues eslint must be run with --fix option.

Using message is pretty useful since it will give a better understanding to the developer when an error happens:

e.g. Given the following definition:

then shown error will be similar to:

or

instead of

or

Definition of the Function used to replace the *invalid* found pattern

Definition of the function must be done as a string in 1 line, and the following rules apply:

• It must return a string value, if not, return value will be ignored, i.e. it will silently fail. • Its definition must be only the body of the function. • For "simple" functions where the return is found at the beginning of the body of the function and the exact word *return* is not present, return can be omitted. • If the function has invalid Javascript code, the function will be ignored, i.e. it will silently fail.

Function will receive 3 parameters, to be used as desired:

• text: a string with the value of the invalid text found. • captured: an array of strings with the values of the captured groups for the regex. • $: an array of strings, with the value of the invalid text found plus the values of the captured groups for the regex, i.e. • $[0] = text: a string with the value of the invalid text found. • $[1..] = captured: an array of strings with the values of the captured groups for the regex. • $[1] = captured[0] and so on. • It allows smaller definitions.

Using parameter text

e.g.

"return text.trim()" => only the body of the function + returns a string value based on text

Having the following rule in .eslintrc.json:

or using $:

then, given:

example.js

when linting with fix, the result will be:…

Description from the npm listing.