Rule: strict-boolean-expressions

Restricts the types allowed in boolean expressions. By default only booleans are allowed.

The following nodes are checked:

• Arguments to the !, &&, and || operators
• The condition in a conditional expression (cond ? x : y)
• Conditions for if, for, while, and do-while statements.

Notes:

Config

These options may be provided:

• allow-null-union allows union types containing null.
  • It does not allow null itself.
  • Without the ‘–strictNullChecks’ compiler option, this will allow anything other than a string, number, or enum.
• allow-undefined-union allows union types containing undefined.
  • It does not allow undefined itself.
  • Without the ‘–strictNullChecks’ compiler option, this will allow anything other than a string, number, or enum.
• allow-string allows strings.
  • It does not allow unions containing string.
  • It does not allow string literal types.
• allow-enum allows enums.
  • It does not allow unions containing enum.
• allow-number allows numbers.
  • It does not allow unions containing number.
  • It does not allow enums or number literal types.
• allow-mix allows multiple of the above to appear together.
  • For example, string | number or RegExp | null | undefined would normally not be allowed.
  • A type like "foo" | "bar" | undefined is always allowed, because it has only one way to be false.
• allow-boolean-or-undefined allows boolean | undefined.
  • Also allows true | false | undefined.
  • Does not allow false | undefined.
  • This option is a subset of allow-undefined-union, so you don’t need to enable both options at the same time.
• ignore-rhs ignores the right-hand operand of && and ||.

Config examples

"strict-boolean-expressions": true

"strict-boolean-expressions": [
  true,
  "allow-null-union",
  "allow-undefined-union",
  "allow-string",
  "allow-enum",
  "allow-number"
]

"strict-boolean-expressions": [true, "allow-boolean-or-undefined"]

Schema

{
  "type": "array",
  "items": {
    "type": "string",
    "enum": [
      "allow-null-union",
      "allow-undefined-union",
      "allow-string",
      "allow-enum",
      "allow-number",
      "allow-boolean-or-undefined",
      "ignore-rhs"
    ]
  },
  "minLength": 0,
  "maxLength": 7
}