is-only

IsOnly - validator

Lightweight TypeScript validation library with fluent API.

API Reference

isOnly.String(val)

Validates non-empty strings.

Returns true for:

• 'hello'
• ' test '

Returns false for:

• '' (empty string)
• ' ' (only spaces)
• null, undefined, different types

isOnly.Number(val)

Validates valid numbers (excluding zero and NaN).

Returns true for:

• 1
• -5
• 3.14

Returns false for:

• '123' (string)
• 0 (zero)
• NaN (not a number)
• null, undefined, different types

isOnly.Boolean(val)

Validates boolean true values only.

Returns true for:

• true

Returns false for:

• false
• 1, 0, 'true', null, undefined, different types

isOnly.Object(val)

Validates non-empty objects (excluding arrays).

Returns true for:

• {a: 1}
• { key: 'value' }

Returns false for:

• {} (empty object)
• [] (array)
• null, undefined, 'string', 0, different types

isOnly.Array(val)

Validates non-empty arrays.

Returns true for:

• [1, 2, 3]
• ['a']

Returns false for:

• [] (empty array)
• '' (empty string)
• ' ' (only spaces)
• null, undefined, different types

isOnly.Failure(val)

Returns true for values that fail all other validations.

Returns true for:

• null, undefined
• '', ' '
• 0, false
• {}, []

Returns false for:

• Any value that passes String, Number, Boolean, Object, or Array validation (non-empty values)

Fluent API Methods

Each validator returns a ValidationResult object with additional methods:

Methods

• .value - Returns validated value or null
• .empty - Inverted validation result
• .throw() - Throws error on failure, returns value on success