Add string utility functions: trimStart, trimEnd, trim

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 
 - `splitLines` string utility function
+- `trimStart`, `trimEnd` and `trim` string type utility functions
 
 ### Changed
 

src/lib/string.spec.ts

@@ -1,4 +1,4 @@
-import { isNullOrEmpty, isNullOrWhitespace, capitalize, uncapitalize, truncate, splitLines } from "./string";
+import { isNullOrEmpty, isNullOrWhitespace, capitalize, uncapitalize, truncate, splitLines, trimStart, trimEnd, trim } from "./string";
 
 describe("string tests", () => {
   test.each([
@@ -121,6 +121,42 @@ describe("string tests", () => {
     expect(truncate(value, maxLength)).toBe(expected);
   });
 
+  test.each([
+    [null as unknown as string, " ", null as unknown as string],
+    [undefined as unknown as string, " ", undefined as unknown as string],
+    ["hello world", "hello world", ""],
+    ["hello world", " ", "hello world"],
+    [" hello world", " ", "hello world"],
+    ["hello world hello world", "hello world", " hello world"],
+    ["hello worldhello world", "hello world", ""],
+  ])("left trim", (haystack, needle, expected) => {
+    expect(trimStart(haystack, needle)).toBe(expected);
+  });
+
+  test.each([
+    [null as unknown as string, " ", null as unknown as string],
+    [undefined as unknown as string, " ", undefined as unknown as string],
+    ["hello world", "hello world", ""],
+    ["hello world ", " ", "hello world"],
+    ["hello world", " ", "hello world"],
+    ["hello world hello world", "hello world", "hello world "],
+    ["hello worldhello world", "hello world", ""],
+  ])("right trim", (haystack, needle, expected) => {
+    expect(trimEnd(haystack, needle)).toBe(expected);
+  });
+
+  test.each([
+    [null as unknown as string, " ", null as unknown as string],
+    [undefined as unknown as string, " ", undefined as unknown as string],
+    ["hello world", "", "hello world"],
+    [" hello world ", " ", "hello world"],
+    ["hello world ", " ", "hello world"],
+    [" hello world", " ", "hello world"],
+    ["hello worldhello world", "hello world", ""],
+  ])("trim", (haystack, needle, expected) => {
+    expect(trim(haystack, needle)).toBe(expected);
+  });
+
   test.each([
     ["", false, false, []],
     [null as unknown as string, false, false, []],

src/lib/string.ts

@@ -65,6 +65,64 @@ export function truncate(value: string | undefined, maxLength: number, suffix =
   return `${value.slice(0, maxLength)}${suffix}`;
 }
 
+/**
+ * Removes all occurrences of needle from the start of haystack
+ * @param haystack string to trim
+ * @param needle the thing to trim
+ * @returns the string trimmed from the left side
+ */
+export function trimStart(haystack: string, needle: string): string {
+  if (isNullOrEmpty(haystack) || isNullOrEmpty(needle)) {
+    return haystack;
+  }
+
+  let offset = 0;
+
+  while (haystack.indexOf(needle, offset) === offset) {
+    offset = offset + needle.length;
+  }
+  return haystack.slice(offset);
+}
+
+/**
+ * Removes all occurrences of needle from the end of haystack
+ * @param haystack string to trim
+ * @param needle the thing to trim
+ * @returns the string trimmed from the right side
+ */
+export function trimEnd(haystack: string, needle: string): string {
+  if (isNullOrEmpty(haystack) || isNullOrEmpty(needle)) {
+    return haystack;
+  }
+
+  let offset = haystack.length,
+    idx = -1;
+
+  while (true) {
+    idx = haystack.lastIndexOf(needle, offset - 1);
+    if (idx === -1 || idx + needle.length !== offset) {
+      break;
+    }
+    if (idx === 0) {
+      return "";
+    }
+    offset = idx;
+  }
+
+  return haystack.slice(0, offset);
+}
+
+/**
+ * Removes all occurrences of needle from the start and the end of haystack
+ * @param haystack string to trim
+ * @param needle the thing to trim
+ * @returns the string trimmed from the right and left side
+ */
+export function trim(haystack: string, needle: string): string {
+  const trimmed = trimStart(haystack, needle);
+  return trimEnd(trimmed, needle);
+}
+
 /**
  * Splits the string at line breaks
  * @param str the string to split