Add string utility functions: ltrim, rtrim, trim (#29)

Author: dom-baur

src/lib/string.spec.ts

@@ -1,4 +1,4 @@
-import { isNullOrEmpty, isNullOrWhitespace, capitalize, uncapitalize, truncate } from "./string";
+import { isNullOrEmpty, isNullOrWhitespace, capitalize, uncapitalize, truncate, ltrim, rtrim, trim } from "./string";
 
 describe("string tests", () => {
   test.each([
@@ -120,4 +120,64 @@ describe("string tests", () => {
   ])("truncate without suffix parameter", (value, maxLength, expected) => {
     expect(truncate(value, maxLength)).toBe(expected);
   });
+
+  test.each([
+    [null as unknown as string, " ", null],
+    [undefined as unknown as string, " ", undefined],
+    [" hello world", " ", "hello world"],
+    ["  hello world", " ", "hello world"],
+    ["   hello world", " ", "hello world"],
+  ])("left trim", (haystack, needle, expected) => {
+    expect(ltrim(haystack, needle)).toBe(expected);
+  });
+
+  test.each([
+    [null as unknown as string, " ", null],
+    [undefined as unknown as string, " ", undefined],
+    [" hello world", "", " hello world"],
+    ["  hello world", "", "  hello world"],
+    ["   hello world", "", "   hello world"],
+  ])("left trim without needle", (haystack, needle, expected) => {
+    expect(ltrim(haystack, needle)).toBe(expected);
+  });
+
+  test.each([
+    [null as unknown as string, " ", null],
+    [undefined as unknown as string, " ", undefined],
+    ["hello world ", " ", "hello world"],
+    ["hello world  ", " ", "hello world"],
+    ["hello world   ", " ", "hello world"],
+  ])("right trim", (haystack, needle, expected) => {
+    expect(rtrim(haystack, needle)).toBe(expected);
+  });
+
+  test.each([
+    [null as unknown as string, " ", null],
+    [undefined as unknown as string, " ", undefined],
+    ["hello world ", "", "hello world "],
+    ["hello world  ", "", "hello world  "],
+    ["hello world   ", "", "hello world   "],
+  ])("right trim without needle", (haystack, needle, expected) => {
+    expect(rtrim(haystack, needle)).toBe(expected);
+  });
+
+  test.each([
+    [null as unknown as string, " ", null],
+    [undefined as unknown as string, " ", undefined],
+    [" hello world ", " ", "hello world"],
+    ["  hello world  ", " ", "hello world"],
+    ["   hello world   ", " ", "hello world"],
+  ])("trim", (haystack, needle, expected) => {
+    expect(trim(haystack, needle)).toBe(expected);
+  });
+
+  test.each([
+    [null as unknown as string, " ", null],
+    [undefined as unknown as string, " ", undefined],
+    [" hello world ", "", " hello world "],
+    ["  hello world  ", "", "  hello world  "],
+    ["   hello world   ", "", "   hello world   "],
+  ])("trim without needle", (haystack, needle, expected) => {
+    expect(trim(haystack, needle)).toBe(expected);
+  });
 });

src/lib/string.ts

@@ -64,3 +64,71 @@ 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 ltrim(haystack: string, needle: string): string {
+  if (!haystack || !needle) return haystack;
+
+  const needleLength = needle.length;
+  if (needleLength === 0 || haystack.length === 0) {
+    return haystack;
+  }
+
+  let offset = 0;
+
+  while (haystack.indexOf(needle, offset) === offset) {
+    offset = offset + needleLength;
+  }
+  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 rtrim(haystack: string, needle: string): string {
+  if (!haystack || !needle) {
+    return haystack;
+  }
+
+  const needleLength = needle.length,
+    haystackLen = haystack.length;
+
+  if (needleLength === 0 || haystackLen === 0) {
+    return haystack;
+  }
+
+  let offset = haystackLen,
+    idx = -1;
+
+  while (true) {
+    idx = haystack.lastIndexOf(needle, offset - 1);
+    if (idx === -1 || idx + needleLength !== 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 = ltrim(haystack, needle);
+  return rtrim(trimmed, needle);
+}