`as const` freezes a value as deeply readonly and infers the narrowest possible literal types. Replaces enums for most use cases — better tree-shaking, no runtime cost.
TypeScript
// Without `as const`: type widens to string[]
const ROLES = ['admin', 'editor', 'viewer'];
type Role = typeof ROLES[number]; // string ❌
// With `as const`: type is the readonly tuple
const ROLES_C = ['admin', 'editor', 'viewer'] as const;
type RoleC = typeof ROLES_C[number]; // 'admin' | 'editor' | 'viewer' ✓
// Same trick for record-style config objects:
const COLORS = {
primary: '#3b82f6',
danger: '#ef4444',
success: '#10b981',
} as const;
type ColorName = keyof typeof COLORS; // 'primary' | 'danger' | 'success'
type ColorHex = typeof COLORS[ColorName]; // '#3b82f6' | '#ef4444' | '#10b981'Save your own code snippets
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