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disallow irregular whitespace (no-irregular-whitespace)

Invalid or irregular whitespace causes issues with ECMAScript 5 parsers and also makes code harder to debug in a similar nature to mixed tabs and spaces.

Various whitespace characters can be inputted by programmers by mistake for example from copying or keyboard shortcuts. Pressing Alt + Space on macOS adds in a non breaking space character for example.

A simple fix for this problem could be to rewrite the offending line from scratch. This might also be a problem introduced by the text editor: if rewriting the line does not fix it, try using a different editor.

Known issues these spaces cause:

  • Zero Width Space
    • Is NOT considered a separator for tokens and is often parsed as an Unexpected token ILLEGAL
    • Is NOT shown in modern browsers making code repository software expected to resolve the visualization
  • Line Separator
    • Is NOT a valid character within JSON which would cause parse errors

Rule Details

This rule is aimed at catching invalid whitespace that is not a normal tab and space. Some of these characters may cause issues in modern browsers and others will be a debugging issue to spot.

This rule disallows the following characters except where the options allow:

\u000B - Line Tabulation (\v) - <VT>
\u000C - Form Feed (\f) - <FF>
\u00A0 - No-Break Space - <NBSP>
\u0085 - Next Line
\u1680 - Ogham Space Mark
\u180E - Mongolian Vowel Separator - <MVS>
\ufeff - Zero Width No-Break Space - <BOM>
\u2000 - En Quad
\u2001 - Em Quad
\u2002 - En Space - <ENSP>
\u2003 - Em Space - <EMSP>
\u2004 - Tree-Per-Em
\u2005 - Four-Per-Em
\u2006 - Six-Per-Em
\u2007 - Figure Space
\u2008 - Punctuation Space - <PUNCSP>
\u2009 - Thin Space
\u200A - Hair Space
\u200B - Zero Width Space - <ZWSP>
\u2028 - Line Separator
\u2029 - Paragraph Separator
\u202F - Narrow No-Break Space
\u205f - Medium Mathematical Space
\u3000 - Ideographic Space

Options

This rule has an object option for exceptions:

  • "skipStrings": true (default) allows any whitespace characters in string literals
  • "skipComments": true allows any whitespace characters in comments
  • "skipRegExps": true allows any whitespace characters in regular expression literals
  • "skipTemplates": true allows any whitespace characters in template literals

skipStrings

Examples of incorrect code for this rule with the default { "skipStrings": true } option:

/*eslint no-irregular-whitespace: "error"*/

function thing() /*<NBSP>*/{
    return 'test';
}

function thing( /*<NBSP>*/){
    return 'test';
}

function thing /*<NBSP>*/(){
    return 'test';
}

function thing᠎/*<MVS>*/(){
    return 'test';
}

function thing() {
    return 'test'; /*<ENSP>*/
}

function thing() {
    return 'test'; /*<NBSP>*/
}

function thing() {
    // Description <NBSP>: some descriptive text
}

/*
Description <NBSP>: some descriptive text
*/

function thing() {
    return / <NBSP>regexp/;
}

/*eslint-env es6*/
function thing() {
    return `template <NBSP>string`;
}

Examples of correct code for this rule with the default { "skipStrings": true } option:

/*eslint no-irregular-whitespace: "error"*/

function thing() {
    return ' <NBSP>thing';
}

function thing() {
    return '​<ZWSP>thing';
}

function thing() {
    return 'th <NBSP>ing';
}

skipComments

Examples of additional correct code for this rule with the { "skipComments": true } option:

/*eslint no-irregular-whitespace: ["error", { "skipComments": true }]*/

function thing() {
    // Description <NBSP>: some descriptive text
}

/*
Description <NBSP>: some descriptive text
*/

skipRegExps

Examples of additional correct code for this rule with the { "skipRegExps": true } option:

/*eslint no-irregular-whitespace: ["error", { "skipRegExps": true }]*/

function thing() {
    return / <NBSP>regexp/;
}

skipTemplates

Examples of additional correct code for this rule with the { "skipTemplates": true } option:

/*eslint no-irregular-whitespace: ["error", { "skipTemplates": true }]*/
/*eslint-env es6*/

function thing() {
    return `template <NBSP>string`;
}

When Not To Use It

If you decide that you wish to use whitespace other than tabs and spaces outside of strings in your application.

Further Reading