noUselessStringConcat (JavaScript)

Language JavaScript (and super languages)

Summary

Rule available since: v1.8.0
Diagnostic Category: lint/complexity/noUselessStringConcat
This rule isn’t recommended, so you need to enable it.
This rule has a safe fix.
The default severity of this rule is information.
Sources:
- Same as no-useless-concat

How to configure

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{
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  "linter": {
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    "rules": {
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      "complexity": {
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        "noUselessStringConcat": "error"
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      }
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    }
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  }
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}

Description

Disallow unnecessary concatenation of string or template literals.

This rule aims to flag concatenation of string or template literals when they could be combined into a single literal. Notably, this also includes concatenating a string with a number (unlike the derivative ESLint rule).

Concatenations split across multiple lines are allowed (such as ones used to prevent exceeding the maximum line width).

Examples

Invalid

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const a = "a" + "b";

code-block.js:1:11 lint/complexity/noUselessStringConcat  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Useless string concatenation.
  
  > 1 │ const a = "a" + "b";
      │           ^^^^^^^^^
    2 │ 
  
  ℹ Consider turning the expression into a single string to improve readability and runtime performance.
  
  ℹ Safe fix: Remove the useless concatenation
  
    1   │ - const·a·=·"a"·+·"b";
      1 │ + const·a·=·"ab";
    2 2 │

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const foo = "string" + 123;

code-block.js:1:13 lint/complexity/noUselessStringConcat  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Useless string concatenation.
  
  > 1 │ const foo = "string" + 123;
      │             ^^^^^^^^^^^^^^
    2 │ 
  
  ℹ Consider turning the expression into a single string to improve readability and runtime performance.
  
  ℹ Safe fix: Remove the useless concatenation
  
    1   │ - const·foo·=·"string"·+·123;
      1 │ + const·foo·=·"string123";
    2 2 │

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const a = "a" + "b" + "c";

code-block.js:1:11 lint/complexity/noUselessStringConcat  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Useless string concatenation.
  
  > 1 │ const a = "a" + "b" + "c";
      │           ^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ Consider turning the expression into a single string to improve readability and runtime performance.
  
  ℹ Safe fix: Remove the useless concatenation
  
    1   │ - const·a·=·"a"·+·"b"·+·"c";
      1 │ + const·a·=·"abc";
    2 2 │

1
const a = (foo + "a") + ("b" + "c");

code-block.js:1:26 lint/complexity/noUselessStringConcat  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Useless string concatenation.
  
  > 1 │ const a = (foo + "a") + ("b" + "c");
      │                          ^^^^^^^^^
    2 │ 
  
  ℹ Consider turning the expression into a single string to improve readability and runtime performance.
  
  ℹ Safe fix: Remove the useless concatenation
  
    1   │ - const·a·=·(foo·+·"a")·+·("b"·+·"c");
      1 │ + const·a·=·(foo·+·"a")·+·("bc");
    2 2 │

Valid

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const a = 1 + 1;

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const a = 1 * '2';

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const a = 1 - 2;

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const a = foo + bar;

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const a = 'foo' + bar;

Multi-line strings are ignored:

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const multiline = 'foo' + // formatting
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          'bar'

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const alsoMultiline = 'foo'
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          + 'bar'
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          + `baz`