useCollapsedIf

Diagnostic Category: lint/nursery/useCollapsedIf

JavaScript (and super languages)

Since: v1.9.4

Sources:

Same as: unicorn/no-lonely-if
Same as: collapsible_if

Description

Enforce using single if instead of nested if clauses.

If an if (b) statement is the only statement in an if (a) block, it is often clearer to use an if (a && b) form.

Examples

Invalid

if (condition) {
    if (anotherCondition) {
        // ...
    }
}

code-block.js:1:17 lint/nursery/useCollapsedIf  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This if statement can be collapsed into another if statement.
  
  > 1 │ if (condition) {
      │                 
  > 2 │     if (anotherCondition) {
  > 3 │         // …
  > 4 │     }
      │     ^
    5 │ }
    6 │ 
  
  ℹ Safe fix: Use collapsed if instead.
  
    1   │ - if·(condition)·{
    2   │ - ····if·(anotherCondition)·{
      1 │ + if·(condition·&&·anotherCondition)·{
    3 2 │           // …
    4   │ - ····}
    5   │ - }
      3 │ + ····}
    6 4 │

if (condition) {
    // Comment
    if (anotherCondition) {
        // ...
    }
}

code-block.js:1:17 lint/nursery/useCollapsedIf ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ⚠ This if statement can be collapsed into another if statement.
  
  > 1 │ if (condition) {
      │                 
  > 2 │     // Comment
  > 3 │     if (anotherCondition) {
  > 4 │         // …
  > 5 │     }
      │     ^
    6 │ }
    7 │

Valid

if (condition && anotherCondition) {
    // ...
}

if (condition) {
    if (anotherCondition) {
        // ...
    }
    doSomething();
}

if (condition) {
    if (anotherCondition) {
        // ...
    } else {
        // ...
    }
}

How to configure

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