Feature request - `truncate` about moderndash HOT 2 CLOSED

// File truncate.ts

type Options = {
  /**
   * The maximum string length.
   *
   * Default: 30
   */
  length?: number;

  /**
   * The string to indicate text is omitted.
   *
   * Also named [ellipsis](https://developer.mozilla.org/en-US/docs/Web/CSS/text-overflow)
   *
   * Default: "...", you might want to use "…" (… U+02026) instead
   */
  omission?: string;

  /**
   * The separator pattern to truncate to.
   *
   * Default: none
   */
  separator?: string;
};

/**
 * Truncates a string if it's longer than the given maximum length.
 * The last characters of the truncated string are replaced with the omission
 * string which defaults to "...".
 *
 * @param str The string to truncate
 * @param options The options object
 * @returns The truncated string
 */
export function truncate(str: string, options?: Options) {
  // https://stackoverflow.com/q/1199352
  // https://github.com/Maggi64/moderndash/issues/155
  // https://lodash.com/docs/4.17.15#truncate

  const { length = 30, omission = '...', separator } = options ?? {};

  if (str.length <= length) {
    return str;
  }

  let maxLength = length - omission.length;
  if (maxLength < 0) {
    maxLength = 0;
  }
  const subString = str.slice(
    0,
    // FYI .slice() is OK if maxLength > text.length
    maxLength
  );

  return (separator ? subString.slice(0, subString.lastIndexOf(separator)) : subString) + omission;
}

// File truncate.test.ts

import { truncate } from './truncate';

// Copy-pasted and adapted from https://github.com/lodash/lodash/blob/c7c70a7da5172111b99bb45e45532ed034d7b5b9/test/truncate.spec.js
// See also https://github.com/lodash/lodash/pull/5815

const string = 'hi-diddly-ho there, neighborino';

it('should use a default `length` of `30`', () => {
  expect(truncate(string)).toBe('hi-diddly-ho there, neighbo...');
});

it('should not truncate if `string` is <= `length`', () => {
  expect(truncate(string, { length: string.length })).toBe(string);
  expect(truncate(string, { length: string.length + 2 })).toBe(string);
});

it('should truncate string the given length', () => {
  expect(truncate(string, { length: 24 })).toBe('hi-diddly-ho there, n...');
});

it('should support a `omission` option', () => {
  expect(truncate(string, { omission: ' [...]' })).toBe('hi-diddly-ho there, neig [...]');
});

it('should support empty `omission` option', () => {
  expect(truncate(string, { omission: '' })).toBe('hi-diddly-ho there, neighborin');
});

it('should support a `length` option', () => {
  expect(truncate(string, { length: 4 })).toBe('h...');
});

it('should support a `separator` option', () => {
  expect(truncate(string, { length: 24, separator: ' ' })).toBe('hi-diddly-ho there,...');
});

it('should treat negative `length` as `0`', () => {
  [0, -2].forEach(length => {
    expect(truncate(string, { length })).toBe('...');
  });
});

it('should work as an iteratee for methods like `_.map`', () => {
  const actual = [string, string, string].map(str => truncate(str));
  const truncated = 'hi-diddly-ho there, neighbo...';

  expect(actual).toEqual([truncated, truncated, truncated]);
});