feat: add padStart and padEnd methods

README.md

@@ -95,6 +95,8 @@ npm install string-ts
   - [endsWith](#endsWith)
   - [join](#join)
   - [length](#length)
+  - [padEnd](#padend)
+  - [padStart](#padstart)
   - [repeat](#repeat)
   - [replace](#replace)
   - [replaceAll](#replaceall)
@@ -225,6 +227,30 @@ const result = length(str)
 //    ^ 5
 ```
 
+### padEnd
+
+This function is a strongly-typed counterpart of `String.prototype.padEnd`.
+
+```ts
+import { padEnd } from 'string-ts'
+
+const str = 'hello'
+const result = padEnd(str, 10, '=')
+//    ^ 'hello====='
+```
+
+### padStart
+
+This function is a strongly-typed counterpart of `String.prototype.padStart`.
+
+```ts
+import { padStart } from 'string-ts'
+
+const str = 'hello'
+const result = padStart(str, 10, '=')
+//    ^ '=====hello'
+```
+
 ### repeat
 
 This function is a strongly-typed counterpart of `String.prototype.repeat`.
@@ -683,6 +709,8 @@ St.Concat<['a', 'bc', 'def']> // 'abcdef'
 St.EndsWith<'abc', 'c'> // true
 St.Join<['hello', 'world'], '-'> // 'hello-world'
 St.Length<'hello'> // 5
+St.PadEnd<'hello', 10, '='> // 'hello====='
+St.PadStart<'hello', 10, '='> // '=====hello'
 St.Repeat<'abc', 3> // 'abcabcabc'
 St.Replace<'hello-world', 'l', '1'> // 'he1lo-world'
 St.ReplaceAll<'hello-world', 'l', '1'> // 'he11o-wor1d'

src/index.ts

@@ -5,6 +5,8 @@ export type {
   EndsWith,
   Join,
   Length,
+  PadEnd,
+  PadStart,
   Repeat,
   Replace,
   ReplaceAll,
@@ -21,6 +23,8 @@ export {
   endsWith,
   join,
   length,
+  padEnd,
+  padStart,
   repeat,
   replace,
   replaceAll,

src/math.ts

@@ -7,17 +7,17 @@ namespace Math {
     B extends number,
   > = TupleOf<A> extends [...infer U, ...TupleOf<B>] ? U['length'] : 0
 
-  export type IsPositive<T extends number> = `${T}` extends `-${number}`
-    ? false
-    : true
+  export type IsNegative<T extends number> = `${T}` extends `-${number}`
+    ? true
+    : false
 
   export type Abs<T extends number> =
     `${T}` extends `-${infer U extends number}` ? U : T
 
   export type GetPositiveIndex<
     T extends string,
     I extends number,
-  > = IsPositive<I> extends true ? I : Subtract<Length<T>, Abs<I>>
+  > = IsNegative<I> extends false ? I : Subtract<Length<T>, Abs<I>>
 }
 
 export type { Math }

src/primitives.test.ts

@@ -79,7 +79,81 @@ describe('primitives', () => {
     })
   })
 
-  test('repeat', () => {
+  describe('padEnd', () => {
+    test('should pad a string at the end', () => {
+      const data = 'hello'
+      const result = subject.padEnd(data, 10)
+      expect(result).toEqual('hello     ')
+      type test = Expect<Equal<typeof result, 'hello     '>>
+    })
+
+    test('should pad with a given string', () => {
+      const data = 'hello'
+      const result = subject.padEnd(data, 10, '=>')
+      expect(result).toEqual('hello=>=>=')
+      type test = Expect<Equal<typeof result, 'hello=>=>='>>
+    })
+
+    test('should not pad if no arguments are given', () => {
+      const data = 'hello'
+      const result = subject.padEnd(data)
+      expect(result).toEqual('hello')
+      type test = Expect<Equal<typeof result, 'hello'>>
+    })
+
+    test('should not pad or truncate if length is shorter than string', () => {
+      const data = 'hello'
+      const result = subject.padEnd(data, 3, '=')
+      expect(result).toEqual('hello')
+      type test = Expect<Equal<typeof result, 'hello'>>
+    })
+
+    test('should not pad for negative numbers', () => {
+      const data = 'hello'
+      const result = subject.padEnd(data, -1, '=')
+      expect(result).toEqual('hello')
+      type test = Expect<Equal<typeof result, 'hello'>>
+    })
+  })
+
+  describe('padStart', () => {
+    test('should pad a string at the start', () => {
+      const data = 'hello'
+      const result = subject.padStart(data, 10)
+      expect(result).toEqual('     hello')
+      type test = Expect<Equal<typeof result, '     hello'>>
+    })
+
+    test('should pad with a given string', () => {
+      const data = 'hello'
+      const result = subject.padStart(data, 10, '=>')
+      expect(result).toEqual('=>=>=hello')
+      type test = Expect<Equal<typeof result, '=>=>=hello'>>
+    })
+
+    test('should not pad if no arguments are given', () => {
+      const data = 'hello'
+      const result = subject.padStart(data)
+      expect(result).toEqual('hello')
+      type test = Expect<Equal<typeof result, 'hello'>>
+    })
+
+    test('should not pad or truncate if length is shorter than string', () => {
+      const data = 'hello'
+      const result = subject.padStart(data, 3, '=')
+      expect(result).toEqual('hello')
+      type test = Expect<Equal<typeof result, 'hello'>>
+    })
+
+    test('should not pad for negative numbers', () => {
+      const data = 'hello'
+      const result = subject.padStart(data, -1, '=')
+      expect(result).toEqual('hello')
+      type test = Expect<Equal<typeof result, 'hello'>>
+    })
+  })
+
+  describe('repeat', () => {
     test('should repeat the string by a given number of times', () => {
       const data = 'abc'
       const result = subject.repeat(data, 3)
@@ -101,7 +175,7 @@ describe('primitives', () => {
     })
   })
 
-  test('replace', () => {
+  describe('replace', () => {
     test('should replace chars in a string at both type level and runtime level once', () => {
       const data = 'some nice string'
       const result = subject.replace(data, ' ')
@@ -110,7 +184,7 @@ describe('primitives', () => {
     })
   })
 
-  test('replaceAll', () => {
+  describe('replaceAll', () => {
     test('should replace all chars in a string at both type level and runtime level once', () => {
       const data = 'some nice string'
       const result = subject.replaceAll(data, ' ')
@@ -190,7 +264,7 @@ describe('primitives', () => {
     })
   })
 
-  test('split', () => {
+  describe('split', () => {
     test('should split a string by a delimiter into an array of substrings', () => {
       const data = 'some nice string'
       const result = subject.split(data, ' ')
@@ -296,7 +370,7 @@ describe('primitives', () => {
     })
   })
 
-  test('trimStart', () => {
+  describe('trimStart', () => {
     test('should trim the start of a string at both type level and runtime level', () => {
       const data = ' some nice string '
       const result = subject.trimStart(data)
@@ -305,7 +379,7 @@ describe('primitives', () => {
     })
   })
 
-  test('trimEnd', () => {
+  describe('trimEnd', () => {
     test('should trim the end of a string at both type level and runtime level', () => {
       const data = ' some nice string '
       const result = subject.trimEnd(data)
@@ -314,7 +388,7 @@ describe('primitives', () => {
     })
   })
 
-  test('trim', () => {
+  describe('trim', () => {
     test('should trim a string at both type level and runtime level', () => {
       const data = ' some nice string '
       const result = subject.trim(data)

src/primitives.ts

@@ -47,7 +47,7 @@ type EndsWith<
   T extends string,
   S extends string,
   P extends number = Length<T>,
-> = Math.IsPositive<P> extends true
+> = Math.IsNegative<P> extends false
   ? P extends Length<T>
     ? S extends Slice<T, Math.Subtract<Length<T>, Length<S>>, Length<T>>
       ? true
@@ -118,15 +118,77 @@ function length<T extends string>(str: T) {
   return str.length as Length<T>
 }
 
+/**
+ * Pads a string at the end with another string.
+ * T: The string to pad.
+ * times: The number of times to pad.
+ * pad: The string to pad with.
+ */
+type PadEnd<
+  T extends string,
+  times extends number = 0,
+  pad extends string = ' ',
+> = Math.IsNegative<times> extends false
+  ? Math.Subtract<times, Length<T>> extends infer missing extends number
+    ? `${T}${Slice<Repeat<pad, missing>, 0, missing>}`
+    : never
+  : T
+/**
+ * A strongly-typed version of `String.prototype.padEnd`.
+ * @param str the string to pad.
+ * @param length the length to pad.
+ * @param pad the string to pad with.
+ * @returns the padded string in both type level and runtime.
+ * @example padEnd('hello', 10, '=') // 'hello====='
+ */
+function padEnd<T extends string, N extends number = 0, U extends string = ' '>(
+  str: T,
+  length: N = 0 as N,
+  pad: U = ' ' as U,
+) {
+  return str.padEnd(length, pad) as PadEnd<T, N, U>
+}
+
+/**
+ * Pads a string at the start with another string.
+ * T: The string to pad.
+ * times: The number of times to pad.
+ * pad: The string to pad with.
+ */
+type PadStart<
+  T extends string,
+  times extends number = 0,
+  pad extends string = ' ',
+> = Math.IsNegative<times> extends false
+  ? Math.Subtract<times, Length<T>> extends infer missing extends number
+    ? `${Slice<Repeat<pad, missing>, 0, missing>}${T}`
+    : never
+  : T
+/**
+ * A strongly-typed version of `String.prototype.padStart`.
+ * @param str the string to pad.
+ * @param length the length to pad.
+ * @param pad the string to pad with.
+ * @returns the padded string in both type level and runtime.
+ * @example padStart('hello', 10, '=') // '=====hello'
+ */
+function padStart<
+  T extends string,
+  N extends number = 0,
+  U extends string = ' ',
+>(str: T, length: N = 0 as N, pad: U = ' ' as U) {
+  return str.padStart(length, pad) as PadStart<T, N, U>
+}
+
 /**
  * Repeats a string N times.
  * T: The string to repeat.
  * N: The number of times to repeat.
  */
-type Repeat<T extends string, N extends number = 0> = N extends 0
+type Repeat<T extends string, times extends number = 0> = times extends 0
   ? ''
-  : Math.IsPositive<N> extends true
-  ? Join<TupleOf<N, T>>
+  : Math.IsNegative<times> extends false
+  ? Join<TupleOf<times, T>>
   : never
 /**
  * A strongly-typed version of `String.prototype.repeat`.
@@ -286,7 +348,7 @@ type StartsWith<
   T extends string,
   S extends string,
   P extends number = 0,
-> = Math.IsPositive<P> extends true
+> = Math.IsNegative<P> extends false
   ? P extends 0
     ? T extends `${S}${string}`
       ? true
@@ -364,6 +426,8 @@ export type {
   EndsWith,
   Join,
   Length,
+  PadEnd,
+  PadStart,
   Repeat,
   Replace,
   ReplaceAll,
@@ -380,6 +444,8 @@ export {
   endsWith,
   join,
   length,
+  padEnd,
+  padStart,
   repeat,
   replace,
   replaceAll,