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Strongly-typed string functions for all!

😬 The problem

When you are working with literal strings, the string manipulation functions only work at the runtime level and the types don't follow those transformations. You end up losing type information and possibly having to cast the result.

const str = 'hello-world';
const result = str.replace('-', ' '); // you should use: as 'hello world'
//    ^? string

🤓 The solution

This library aims to solve this problem by providing a set of common functions that work with literal strings at both type and runtime level.

import { replace } from 'string-ts';

const str = 'hello-world';
const result = replace(str, '-', ' ');
//    ^ 'hello world'

📦 Installation

npm install string-ts

📖 API

Runtime counterparts of native type utilities

capitalize

Capitalizes the first letter of a string. This is a runtime counterpart of Capitalize<T> from src/types.d.ts.

import { capitalize } from 'string-ts';

const str = 'hello world';
const result = capitalize(str);
//    ^ 'Hello world'

Strongly-typed alternatives to native runtime utilities

toUpperCase

This function is a strongly-typed counterpart of String.prototype.toUpperCase.

import { toUpperCase } from 'string-ts';

const str = 'hello world';
const result = toUpperCase(str);
//    ^ 'HELLO WORLD'

toLowerCase

This function is a strongly-typed counterpart of String.prototype.toLowerCase.

import { toLowerCase } from 'string-ts';

const str = 'HELLO WORLD';
const result = toLowerCase(str);
//    ^ 'hello world'

trim

This function is a strongly-typed counterpart of String.prototype.trim.

import { trim } from 'string-ts';

const str = '  hello world  ';
const result = trim(str);
//    ^ 'hello world'

trimStart

This function is a strongly-typed counterpart of String.prototype.trimStart.

import { trimStart } from 'string-ts';

const str = '  hello world  ';
const result = trimStart(str);
//    ^ 'hello world  '

trimEnd

This function is a strongly-typed counterpart of String.prototype.trimEnd.

import { trimEnd } from 'string-ts';

const str = '  hello world  ';
const result = trimEnd(str);
//    ^ '  hello world'

join

This function is a strongly-typed counterpart of Array.prototype.join.

import { join } from 'string-ts';

const str = ['hello', 'world'] as ['hello', 'world'];
const result = join(str, ' ');
//    ^ 'hello world'

replace

This function is a strongly-typed counterpart of String.prototype.replace.

import { replace } from 'string-ts';

const str = 'hello-world-';
const result = replace(str, '-', ' ');
//    ^ 'hello world-'

replaceAll

This function is a strongly-typed counterpart of String.prototype.replaceAll.

import { replaceAll } from 'string-ts';

const str = 'hello-world-';
const result = replaceAll(str, '-', ' ');
//    ^ 'hello world '

split

This function is a strongly-typed counterpart of String.prototype.split.

import { split } from 'string-ts';

const str = 'hello-world';
const result = split(str, '-');
//    ^ ['hello', 'world']

Strongly-typed alternatives to common loosely-typed functions

words

This function identifies the words in a string and returns a tuple of words split by separators, differences in casing, numbers, and etc.

import { words } from 'string-ts';

const str = '-20someVery-weird String';
const result = words(str);
//    ^ ['20', 'some', 'Very', 'weird', 'String']

toDelimiterCase

This function converts a string to a new case with a custom delimiter at both runtime and type levels.

import { toDelimiterCase } from 'string-ts';

const str = 'helloWorld';
const result = toDelimiterCase(str, '.');
//    ^ 'hello.World'

toCamelCase

This function converts a string to camelCase at both runtime and type levels.

import { toCamelCase } from 'string-ts';

const str = 'hello-world';
const result = toCamelCase(str);
//    ^ 'helloWorld'

toPascalCase

This function converts a string to PascalCase at both runtime and type levels.

import { toPascalCase } from 'string-ts';

const str = 'hello-world';
const result = toPascalCase(str);
//    ^ 'HelloWorld'

toKebabCase

This function converts a string to kebab-case at both runtime and type levels.

import { toKebabCase } from 'string-ts';

const str = 'helloWorld';
const result = toKebabCase(str);
//    ^ 'hello-world'

toSnakeCase

This function converts a string to snake_case at both runtime and type levels.

import { toSnakeCase } from 'string-ts';

const str = 'helloWorld';
const result = toSnakeCase(str);
//    ^ 'hello_world'

toConstantCase

This function converts a string to CONSTANT_CASE at both runtime and type levels.

import { toConstantCase } from 'string-ts';

const str = 'helloWorld';
const result = toConstantCase(str);
//    ^ 'HELLO_WORLD'

toTitleCase

This function converts a string to Title Case at both runtime and type levels.

import { toTitleCase } from 'string-ts';

const str = 'helloWorld';
const result = toTitleCase(str);
//    ^ 'Hello World'

Strongly-typed deep transformation of objects

deepDelimiterKeys

This function recursively converts the keys of an object to a new case with a custom delimiter at both runtime and type levels.

import { deepDelimiterKeys } from 'string-ts';

const data = {
  'hello-world': {
    'foo-bar': 'baz',
  },
} as const;
const result = deepDelimiterKeys(data, '.');
//    ^ { 'hello.world': { 'foo.bar': 'baz' } }

deepCamelKeys

This function recursively converts the keys of an object to camelCase at both runtime and type levels.

import { deepCamelKeys } from 'string-ts';

const data = {
  'hello-world': {
    'foo-bar': 'baz',
  },
} as const;
const result = deepCamelKeys(data);
//    ^ { helloWorld: { fooBar: 'baz' } }

deepPascalKeys

This function recursively converts the keys of an object to PascalCase at both runtime and type levels.

import { deepPascalKeys } from 'string-ts';

const data = {
  'hello-world': {
    'foo-bar': 'baz',
  },
} as const;
const result = deepPascalKeys(data);
//    ^ { HelloWorld: { FooBar: 'baz' } }

deepKebabKeys

This function recursively converts the keys of an object to kebab-case at both runtime and type levels.

import { deepKebabKeys } from 'string-ts';

const data = {
  'helloWorld': {
    'fooBar': 'baz',
  },
} as const;
const result = deepKebabKeys(data);
//    ^ { 'hello-world': { 'foo-bar': 'baz' } }

deepSnakeKeys

This function recursively converts the keys of an object to snake_case at both runtime and type levels.

import { deepSnakeKeys } from 'string-ts';

const data = {
  'helloWorld': {
    'fooBar': 'baz',
  },
} as const;
const result = deepSnakeKeys(data);
//    ^ { 'hello_world': { 'foo_bar': 'baz' } }

deepConstantKeys

This function recursively converts the keys of an object to CONSTANT_CASE at both runtime and type levels.

import { deepConstantKeys } from 'string-ts';

const data = {
  'helloWorld': {
    'fooBar': 'baz',
  },
} as const;
const result = deepConstantKeys(data);
//    ^ { 'HELLO_WORLD': { 'FOO_BAR': 'baz' } }

Type Utilities

All the functions presented in this API have associated type counterparts.

import type * as St from 'string-ts';

Native TS type utilities

Capitalize<'hello world'> // 'Hello world'
Lowercase<'HELLO WORLD'> // 'hello world'
Uppercase<'hello world'> // 'HELLO WORLD'

General Type utilities from this library

St.Words<'hello-world'> // ['hello', 'world']
St.Join<['hello', 'world'], '-'> // 'hello-world'
St.Replace<'hello-world', 'l', '1'> // 'he1lo-world'
St.ReplaceAll<'hello-world', 'l', '1'> // 'he11o-wor1d'
St.Split<'hello-world', '-'> // ['hello', 'world']
St.TrimStart<' hello world '> // 'hello world '
St.TrimEnd<' hello world '> // ' hello world'
St.Trim<' hello world '> // 'hello world'

Casing type utilities

St.CamelCase<'hello-world'> // 'helloWorld'
St.PascalCase<'hello-world'> // 'HelloWorld'
St.KebabCase<'helloWorld'> // 'hello-world'
St.SnakeCase<'helloWorld'> // 'hello_world'
St.ConstantCase<'helloWorld'> // 'HELLO_WORLD'
St.TitleCase<'helloWorld'> // 'Hello World'
St.DelimiterCase<'hello world', '.'> // 'hello.world'

St.DeepDelimiterKeys<{
  'hello-world': { 'foo-bar': 'baz' }
}, '.'> // { 'hello.world': { 'foo.bar': 'baz' } }
St.DeepCamelKeys<{
  'hello-world': { 'foo-bar': 'baz' }
}> // { helloWorld: { fooBar: 'baz' } }
St.DeepPascalKeys<{
  'hello-world': { 'foo-bar': 'baz' }
}> // { HelloWorld: { FooBar: 'baz' } }
St.DeepKebabKeys<{
  'helloWorld': { 'fooBar': 'baz' }
}> // { 'hello-world': { 'foo-bar': 'baz' } }
St.DeepSnakeKeys<{
  'helloWorld': { 'fooBar': 'baz' }
}> // { 'hello_world': { 'foo_bar': 'baz' } }
St.DeepConstantKeys<{
  'helloWorld': { 'fooBar': 'baz' }
}> // { 'HELLO_WORLD': { 'FOO_BAR': 'baz' } }

Other exported type utilities

St.IsDigit<'a'> // false
St.IsDigit<'1'> // true
St.IsLetter<'a'> // true
St.IsLetter<'1'> // false
St.IsLower<'a'> // true
St.IsLower<'A'> // false
St.IsUpper<'a'> // false
St.IsUpper<'A'> // true
St.IsSeparator<' '> // true
St.IsSeparator<'-'> // true
St.IsSeparator<'a'> // false
St.IsSpecial<'a'> // false
St.IsSpecial<'!'> // true
St.IsSpecial<' '> // false

Runtime-only utilities

deepTransformKeys

This function recursively converts the keys of an object to a custom format, but only at runtime level.

import { deepTransformKeys, toUpperCase } from 'string-ts';

const data = { 'helloWorld': 'baz' } as const;

type MyType<T> = { [K in keyof T as Uppercase<K>]: T[K] }
const result = deepTransformKeys(data, toUpperCase) as MyType<typeof data>;
//    ^ { 'HELLOWORLD': 'baz' }

Disclaimer

This library doesn't support every internal character for the sake of keeping the maintainer's sanity.