WEB422 Summer 2019 Week 7 Code Example: TypeScript

count.ts

/**
 * TypeScript rewrite of https://gist.github.com/humphd/c37e233f57c4b942ac3e8c30fae855f2
 * 
 * Example module to get info about a multi-line string,
 * written as an ES module.
 *
 * Takes a multiline string, and returns an Object:
 *
 * "here is a line of text"
 * 
 * {
 *   lines: [
 *     {
 *       line: "here is a line of text",
 *       count: 17
 *     },
 *     {
 *       line: "here is the 2nd line of text",
 *       count: 17
 *     },
 *      
 *   count: 17
 * }
*/

/**
 * Information about a line of text.
 */
interface LineMetrics {
  line: string,
  count: number,
  number: number
}

/**
 * Information about a multi-line text.
 */
interface TextMetrics {
  lines: LineMetrics[],
  total: number
}

 /** 
 * Split the given string into lines, taking into
 * account Windows (\r\n) vs. Unix (\n) line endings.
 */
const splitIntoLines = (text: string): Array<string> =>
  text.split(/\r?\n/);

/*
 * Count the number of non-whitespace (space, tab, etc)
 * characters in the given string, returning the count
 * "here is a           line of text" -> 17
 */
const countNonWhitespace = (text: string): number =>
  text.replace(/\s+/g, '').length;

/**
 * Process a list of lines (Array of Strings) into an
 * Array of Objects, where each Object has info about
 * the given line:
 * 
 *  - The `line` itself
 *  - The `count` of non-whitespace characters in the line
 *  - The `number` of the line in the string, starting at 1
 */
const processLines = (list: Array<string>): Array<LineMetrics> =>
    list.map((element, index) => {
        return {
            line: element,
            count: countNonWhitespace(element),
            number: index + 1
        };
    });

const getTotalCharacters = (lines: Array<LineMetrics>): number =>
    lines.reduce((total, element) => total + element.count, 0);

/**
 * Main public entry point to the module.  Take
 * the given multi-line string, and produce an Object
 * with info about each line, as well as a total
 * character count for non-whitespace characters.
 */
function processText(text: string): TextMetrics {
    const lines = processLines(splitIntoLines(text));

    return {
        lines,
        total: getTotalCharacters(lines)
    };
}

/**
 * Expose the `processText` function on the module's `exports`
 * Object, making it accessible to callers.  All other functions
 * will remain "hidden" within this module.
 */
export {
  processText,
  TextMetrics
};

index.html

<script src="main.js"></script>

main.ts

import { processText } from './count';

const text: string = `This is the first line.
This is the second line.
This is the final line of the text.`;

console.log(processText(text));

package.json

{
  "name": "words-ts",
  "version": "1.0.0",
  "scripts": {
    "compile": "tsc main",
    "serve": "parcel index.html",
    "start": "npm run compile && npm run serve"
  },
  "devDependencies": {
    "parcel": "^1.12.3",
    "typescript": "^3.5.2"
  }
}