noIncrementDecrement

JavaScript (and super languages)

Caution

This rule is part of the nursery group. This means that it is experimental and the behavior can change at any time.

Summary

• Rule available since: v2.3.2
• Diagnostic Category: lint/nursery/noIncrementDecrement
• This rule doesn’t have a fix.
• The default severity of this rule is information.
• Sources:
  • Same as no-plusplus

How to configure

biome.json

{
  "linter": {
    "rules": {
      "nursery": {
        "noIncrementDecrement": "error"
      }
    }
  }
}

Description

Disallows the usage of the unary operators ++ and —.

Because the unary ++ and — operators are subject to automatic semicolon insertion, differences in whitespace can change semantics of source code.

let i = 10;
let j = 20;

i ++
j
// i = 11, j = 20

code-block.js:4:1 lint/nursery/noIncrementDecrement ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Unexpected use of increment/decrement unary operator.
  
    2 │ let j = 20;
    3 │ 
  > 4 │ i ++
      │ ^^^^
    5 │ j
    6 │ // i = 11, j = 20
  
  ℹ The unary ++ and — operators are subject to automatic semicolon insertion, differences in whitespace can change semantics of source code. Instead use += or -=.
  

let i = 10;
let j = 20;

i
++
j
// i = 10, j = 21

code-block.js:5:1 lint/nursery/noIncrementDecrement ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Unexpected use of increment/decrement unary operator.
  
    4 │ i
  > 5 │ ++
      │ ^^
  > 6 │ j
      │ ^
    7 │ // i = 10, j = 21
    8 │ 
  
  ℹ The unary ++ and — operators are subject to automatic semicolon insertion, differences in whitespace can change semantics of source code. Instead use += or -=.
  

Examples

Invalid

let foo = 0;
foo++;

code-block.js:2:1 lint/nursery/noIncrementDecrement ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Unexpected use of increment/decrement unary operator.
  
    1 │ let foo = 0;
  > 2 │ foo++;
      │ ^^^^^
    3 │ 
  
  ℹ The unary ++ and — operators are subject to automatic semicolon insertion, differences in whitespace can change semantics of source code. Instead use += or -=.
  

let bar = 42;
bar--;

code-block.js:2:1 lint/nursery/noIncrementDecrement ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Unexpected use of increment/decrement unary operator.
  
    1 │ let bar = 42;
  > 2 │ bar—;
      │ ^^^^^
    3 │ 
  
  ℹ The unary ++ and — operators are subject to automatic semicolon insertion, differences in whitespace can change semantics of source code. Instead use += or -=.
  

for (let i = 0; i < 10; i++) {
    doSomething(i);
}

code-block.js:1:25 lint/nursery/noIncrementDecrement ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Unexpected use of increment/decrement unary operator.
  
  > 1 │ for (let i = 0; i < 10; i++) {
      │                         ^^^
    2 │     doSomething(i);
    3 │ }
  
  ℹ The unary ++ and — operators are subject to automatic semicolon insertion, differences in whitespace can change semantics of source code. Instead use += or -=.
  

for (let i = 0; i < 10;) {
    doSomething(i);
    i++;
}

code-block.js:3:5 lint/nursery/noIncrementDecrement ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Unexpected use of increment/decrement unary operator.
  
    1 │ for (let i = 0; i < 10;) {
    2 │     doSomething(i);
  > 3 │     i++;
      │     ^^^
    4 │ }
    5 │ 
  
  ℹ The unary ++ and — operators are subject to automatic semicolon insertion, differences in whitespace can change semantics of source code. Instead use += or -=.
  

Valid

let foo = 0;
foo += 1;

let bar = 42;
bar -= 1;

for (let i = 0; i < 10; i += 1) {
    doSomething(i);
}

for (let i = 0; i < 10;) {
    doSomething(i);
    i += 1;
}

Options

allowForLoopAfterthoughts

Allows unary operators ++ and — in the afterthought (final expression) of a for loop.

Default false

biome.json

{
  "linter": {
    "rules": {
      "nursery": {
        "noIncrementDecrement": {
          "options": {
            "allowForLoopAfterthoughts": true
          }
        }
      }
    }
  }
}

Invalid

for (let i = 0; i < j; j = i++) {
    doSomething(i, j);
}

code-block.js:1:28 lint/nursery/noIncrementDecrement ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Unexpected use of increment/decrement unary operator.
  
  > 1 │ for (let i = 0; i < j; j = i++) {
      │                            ^^^
    2 │     doSomething(i, j);
    3 │ }
  
  ℹ The unary ++ and — operators are subject to automatic semicolon insertion, differences in whitespace can change semantics of source code. Instead use += or -=.
  

for (let i = 10; i--;) {
    doSomething(i);
}

code-block.js:1:18 lint/nursery/noIncrementDecrement ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Unexpected use of increment/decrement unary operator.
  
  > 1 │ for (let i = 10; i—;) {
      │                  ^^^
    2 │     doSomething(i);
    3 │ }
  
  ℹ The unary ++ and — operators are subject to automatic semicolon insertion, differences in whitespace can change semantics of source code. Instead use += or -=.
  

for (let i = 0; i < 10;) i++;

code-block.js:1:26 lint/nursery/noIncrementDecrement ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Unexpected use of increment/decrement unary operator.
  
  > 1 │ for (let i = 0; i < 10;) i++;
      │                          ^^^
    2 │ 
  
  ℹ The unary ++ and — operators are subject to automatic semicolon insertion, differences in whitespace can change semantics of source code. Instead use += or -=.
  

Valid

for (let i = 0; i < 10; i++) {
    doSomething(i);
}

for (let i = 0, j = l; i < l; i++, j--) {
    doSomething(i, j);
}

Related links

• Disable a rule
• Configure the code fix
• Rule options
• Source Code
• Test Cases