feat(utility): add string/substring

.changeset/serious-weeks-jam.md

@@ -0,0 +1,5 @@
+---
+'@xstools/utility': minor
+---
+
+add string/substring

packages/utility/src/string/index.ts

@@ -1,4 +1,5 @@
 export * from './case';
 export * from './getWords';
+export * from './substring';
 export * from './template';
 export * from './trim';

packages/utility/src/string/substring.spec.ts

@@ -0,0 +1,40 @@
+import { describe, expect, test } from 'bun:test';
+import { substring } from './substring';
+
+describe('substring', () => {
+  test('normal usage', () => {
+    expect(substring('123', 2)).toBe('12');
+    expect(substring('123', 10)).toBe('123');
+
+    expect(substring('今天很开心🌸🌸🌸', 6)).toBe('今天很开心🌸');
+    expect('今天很开心🌸🌸🌸'.substring(0, 6)).toBe('今天很开心\ud83c');
+  });
+
+  test('unicode support', () => {
+    expect(substring('𝒽𝑒𝓁𝓁𝑜 𝓌𝑜𝓇𝓁𝒹', 1)).toBe('𝒽');
+    expect('𝒽𝑒𝓁𝓁𝑜 𝓌𝑜𝓇𝓁𝒹'.substring(0, 2)).toBe('𝒽');
+
+    expect(substring('🐶狗', 1)).toBe('🐶');
+    expect('🐶狗'.substring(0, 2)).toBe('🐶');
+
+    expect(substring('狗狗', 1)).toBe('狗');
+    expect('狗狗'.substring(0, 1)).toBe('狗');
+
+    // https://juejin.cn/post/7070079762429034526
+    expect(substring('🐕‍🦺狗', 1)).toBe('🐕');
+    expect('🐕‍🦺狗'.substring(0, 2)).toBe('🐕');
+  });
+
+  test('empty', () => {
+    expect(substring('xxx', 0)).toBe('');
+    expect(substring('', 0)).toBe('');
+    expect(substring('', 10)).toBe('');
+
+    // @ts-expect-error
+    expect(substring({}, 10)).toBe('');
+    // @ts-expect-error
+    expect(substring(1, 10)).toBe('');
+    // @ts-expect-error
+    expect(substring([1], 10)).toBe('');
+  });
+});

packages/utility/src/string/substring.ts

@@ -0,0 +1,21 @@
+/**
+ * Returns the part of this string by length.
+ *
+ * @example
+ * substring('123', 2) // => '12'
+ * substring('123', 10) // => '123'
+ * substring('今天很开心🌸🌸🌸', 6) // => '今天很开心🌸'
+ *
+ * --- WHY NOT NATIVE ---
+ * '今天很开心🌸🌸🌸'.substring(0, 6) // => '今天很开心\ud83c'
+ * '今天很开心🌸🌸🌸'.substring(0, 7) // => '今天很开心🌸'
+ */
+export const substring = (s: string, length: number): string => {
+  if (typeof s !== 'string') {
+    return '';
+  }
+
+  const temp = s.substring(0, length * 2);
+
+  return [...temp].slice(0, length).join('');
+};

packages/utility/src/string/template.spec.ts

@@ -2,7 +2,7 @@ import { describe, expect, test } from 'bun:test';
 import { template } from './template';
 
 describe('template', () => {
-  test('template', () => {
+  test('normal usage', () => {
     expect(template('hello, {{name}}', { name: 'world' })).toBe('hello, world');
     expect(template('hello, {{    name  \n}}', { name: 'world' })).toBe('hello, world');
     expect(template('hello, {{name}}', {})).toBe('hello, ');