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identifier

Accepts and returns strings that are valid identifiers in most programming languages.

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Type Signature

const identifier: Decoder<string>

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Validation Pattern

Validates identifier naming conventions:
  • Must start with a letter (a-z, A-Z) or underscore (_)
  • Followed by any combination of letters, digits (0-9), or underscores
  • Case-insensitive
Regex pattern: 
/^[a-z_][a-z0-9_]*$/i

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Valid Inputs

import { identifier } from 'decoders';

identifier.verify('myVariable');      // ✓ 'myVariable'
identifier.verify('_privateMethod');  // ✓ '_privateMethod'
identifier.verify('user123');         // ✓ 'user123'
identifier.verify('CLASS_NAME');      // ✓ 'CLASS_NAME'
identifier.verify('a');               // ✓ 'a'
identifier.verify('_');               // ✓ '_'
identifier.verify('snake_case_var');  // ✓ 'snake_case_var'
identifier.verify('camelCaseVar');    // ✓ 'camelCaseVar'
identifier.verify('PascalCase');      // ✓ 'PascalCase'

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Invalid Inputs

identifier.verify('123abc');          // ✗ Must be valid identifier (starts with digit)
identifier.verify('my-variable');     // ✗ Must be valid identifier (contains hyphen)
identifier.verify('my.variable');     // ✗ Must be valid identifier (contains dot)
identifier.verify('my variable');     // ✗ Must be valid identifier (contains space)
identifier.verify('user@name');       // ✗ Must be valid identifier (contains @)
identifier.verify('');                // ✗ Must be valid identifier (empty string)
identifier.verify('$var');            // ✗ Must be valid identifier ($ not allowed)
identifier.verify(123);               // ✗ Must be string

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Error Message

When validation fails: "Must be valid identifier"

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Implementation

export const identifier: Decoder<string> = regex(
  /^[a-z_][a-z0-9_]*$/i,
  'Must be valid identifier',
);
Source: src/strings.ts:98-101

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Use Cases

  • Validating variable names in code generators
  • Checking function or class names
  • Ensuring database column/table names follow conventions
  • Validating API parameter names
  • Configuration key validation

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Notes

  • This pattern matches identifiers in languages like JavaScript, Python, Java, C++, etc.
  • Does not validate against language-specific reserved keywords
  • Does not allow Unicode identifiers (only ASCII)
  • Does not allow dollar signs ($), which are valid in some languages like JavaScript
  • regex - Create custom string pattern validators
  • startsWith - Match strings with specific prefixes
  • endsWith - Match strings with specific suffixes

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