metadata:
  version: "1.0.0"
  last_updated: "2026-02-01"
  source_urls: []

category: language-specific
subcategory: javascript
tier: T2

bugs_caught:
  - "JavaScript type coercion"
  - "Equality comparison bugs"
  - "Truthy/falsy confusion"

values:
  # Equality quirks
  eq_vs_strict:
    comparisons:
      - expr: "0 == ''"
        result: true
      - expr: "0 === ''"
        result: false
    bugs_caught:
      - "== vs === confusion"
      - "Type coercion in comparison"
    safe_for_automation: true

  null_undefined_eq:
    comparisons:
      - expr: "null == undefined"
        result: true
      - expr: "null === undefined"
        result: false
    bugs_caught:
      - "null/undefined equivalence"
    safe_for_automation: true

  array_comparison:
    comparisons:
      - expr: "[] == []"
        result: false
      - expr: "[] == false"
        result: true
      - expr: "[] == ''"
        result: true
    bugs_caught:
      - "Array comparison by reference"
      - "Array coercion"
    safe_for_automation: true

  object_comparison:
    comparisons:
      - expr: "{} == {}"
        result: false
      - expr: "{} == '[object Object]'"
        result: false
    bugs_caught:
      - "Object comparison by reference"
    safe_for_automation: true

  # Type coercion
  plus_operator:
    expressions:
      - expr: "'5' + 3"
        result: "'53'"
      - expr: "5 + '3'"
        result: "'53'"
      - expr: "5 - '3'"
        result: 2
    bugs_caught:
      - "+ operator string coercion"
      - "Inconsistent arithmetic"
    safe_for_automation: true

  array_to_number:
    expressions:
      - expr: "+[]"
        result: 0
      - expr: "+[1]"
        result: 1
      - expr: "+[1,2]"
        result: "NaN"
    bugs_caught:
      - "Array coercion to number"
    safe_for_automation: true

  # Truthy/falsy edge cases
  empty_array_truthy:
    value: "[]"
    truthy: true
    bugs_caught:
      - "Empty array is truthy"
      - "Need length check"
    safe_for_automation: true

  empty_object_truthy:
    value: "{}"
    truthy: true
    bugs_caught:
      - "Empty object is truthy"
      - "Need Object.keys check"
    safe_for_automation: true

  nan_falsy:
    value: "NaN"
    truthy: false
    bugs_caught:
      - "NaN is falsy"
    safe_for_automation: true

  # typeof quirks
  typeof_null:
    expr: "typeof null"
    result: "'object'"
    bugs_caught:
      - "typeof null is 'object'"
    safe_for_automation: true

  typeof_array:
    expr: "typeof []"
    result: "'object'"
    bugs_caught:
      - "Arrays are 'object' not 'array'"
    safe_for_automation: true

  typeof_nan:
    expr: "typeof NaN"
    result: "'number'"
    bugs_caught:
      - "NaN is type 'number'"
    safe_for_automation: true

  # Array methods
  array_sort_numeric:
    expr: "[10, 2, 1].sort()"
    result: "[1, 10, 2]"
    bugs_caught:
      - "Default sort is lexicographic"
    safe_for_automation: true

  array_includes_nan:
    expr: "[NaN].includes(NaN)"
    result: true
    bugs_caught:
      - "includes works with NaN"
    safe_for_automation: true

  array_indexof_nan:
    expr: "[NaN].indexOf(NaN)"
    result: -1
    bugs_caught:
      - "indexOf fails with NaN"
    safe_for_automation: true

  # Number edge cases
  parseint_leading_zero:
    expr: "parseInt('08')"
    result: 8
    bugs_caught:
      - "parseInt octal (fixed in ES5)"
    safe_for_automation: true

  parsefloat_trailing:
    expr: "parseFloat('3.14abc')"
    result: 3.14
    bugs_caught:
      - "parseFloat ignores trailing chars"
    safe_for_automation: true

  number_constructor:
    expressions:
      - expr: "Number('')"
        result: 0
      - expr: "Number(' ')"
        result: 0
      - expr: "Number(null)"
        result: 0
      - expr: "Number(undefined)"
        result: "NaN"
    bugs_caught:
      - "Number() edge cases"
    safe_for_automation: true