Implementing a Simple Fibonacci Sequence Calculator with TypeScript and Node.js

Implementing a Simple Fibonacci Sequence Calculator with TypeScript and Node.js

This article uses TypeScript together with Node.js's built-in readline module to read user input from the terminal and calculate the Fibonacci number at the corresponding position based on the number entered. The goal is to introduce the basic usage of TypeScript and Node.js terminal modules.

1. Project package file: package.json

• This file is generated in the project root directory with the npm init command, and then modified as needed.
• Pay attention to the start script and the watch-ts script. The latter is used to automatically watch for changes in .ts files and compile them, while the former is used to start the program.
• Create two directories, src and dist, under the project root, and create an index.ts file in src as the main project file.

{
  "name": "fibonacci",
  "version": "1.0.0",
  "description": "use typescript to solve fibonacci problem in three ways",
  "main": "dist/index.js",
  "scripts": {
    "start": "npm run serve",
    "test": "echo \"Error: no test specified\" && exit 1",
    "watch-ts": "tsc -w",
    "serve": "node dist/index.js"
  },
  "keywords": [
    "typescript",
    "javascript",
    "npm",
    "fibonacci",
    "yield"
  ],
  "author": "weizy0219",
  "license": "MIT",
  "devDependencies": {
    "@types/node": "^13.11.1",
    "ts-node": "^8.8.2",
    "typescript": "^3.8.3"
  }
}

2. TypeScript configuration file: tsconfig.json

This file is generated in the root directory using the tsc --init command and then modified accordingly.

• In addition to the default compilerOptions, include and exclude are added to specify which folders to include and exclude.

{
  "compilerOptions": {
    /* Basic Options */
    // "incremental": true,                   /* Enable incremental compilation */
    "target": "es5",                          /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', or 'ESNEXT'. */
    "module": "commonjs",                     /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', 'es2020', or 'ESNext'. */
    // "lib": [],                             /* Specify library files to be included in the compilation. */
    // "allowJs": true,                       /* Allow javascript files to be compiled. */
    // "checkJs": true,                       /* Report errors in .js files. */
    // "jsx": "preserve",                     /* Specify JSX code generation: 'preserve', 'react-native', or 'react'. */
    // "declaration": true,                   /* Generates corresponding '.d.ts' file. */
    // "declarationMap": true,                /* Generates a sourcemap for each corresponding '.d.ts' file. */
    "sourceMap": true,                     /* Generates corresponding '.map' file. */
    // "outFile": "./",                       /* Concatenate and emit output to single file. */
    "outDir": "dist",                        /* Redirect output structure to the directory. */
    // "rootDir": "./",                       /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
    // "composite": true,                     /* Enable project compilation */
    // "tsBuildInfoFile": "./",               /* Specify file to store incremental compilation information */
    "removeComments": true,                /* Do not emit comments to output. */
    // "noEmit": true,                        /* Do not emit outputs. */
    // "importHelpers": true,                 /* Import emit helpers from 'tslib'. */
    // "downlevelIteration": true,            /* Provide full support for iterables in 'for-of', spread, and destructuring when targeting 'ES5' or 'ES3'. */
    // "isolatedModules": true,               /* Transpile each file as a separate module (similar to 'ts.transpileModule'). */

    /* Strict Type-Checking Options */
    "strict": true,                           /* Enable all strict type-checking options. */
    "noImplicitAny": true,                 /* Raise error on expressions and declarations with an implied 'any' type. */
    "strictNullChecks": true,              /* Enable strict null checks. */
    // "strictFunctionTypes": true,           /* Enable strict checking of function types. */
    // "strictBindCallApply": true,           /* Enable strict 'bind', 'call', and 'apply' methods on functions. */
    // "strictPropertyInitialization": true,  /* Enable strict checking of property initialization in classes. */
    "noImplicitThis": true,                /* Raise error on 'this' expressions with an implied 'any' type. */
    // "alwaysStrict": true,                  /* Parse in strict mode and emit "use strict" for each source file. */

    /* Additional Checks */
    // "noUnusedLocals": true,                /* Report errors on unused locals. */
    // "noUnusedParameters": true,            /* Report errors on unused parameters. */
    // "noImplicitReturns": true,             /* Report error when not all code paths in function return a value. */
    // "noFallthroughCasesInSwitch": true,    /* Report errors for fallthrough cases in switch statement. */

    /* Module Resolution Options */
    // "moduleResolution": "node",            /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
    // "baseUrl": "./",                       /* Base directory to resolve non-absolute module names. */
    // "paths": {},                           /* A series of entries which re-map imports to lookup locations relative to the 'baseUrl'. */
    // "rootDirs": [],                         /* List of root folders whose combined content represents the structure of the project at runtime. */
    // "typeRoots": [],                       /* List of folders to include type definitions from. */
    // "types": [],                           /* Type declaration files to be included in compilation. */
    // "allowSyntheticDefaultImports": true,  /* Allow default imports from modules with no default export. This does not affect code emit, just typechecking. */
    "esModuleInterop": true,                  /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
    // "preserveSymlinks": true,              /* Do not resolve the real path of symlinks. */
    // "allowUmdGlobalAccess": true,          /* Allow accessing UMD globals from modules. */

    /* Source Map Options */
    // "sourceRoot": "",                      /* Specify the location where debugger should locate TypeScript files instead of source locations. */
    // "mapRoot": "",                         /* Specify the location where debugger should locate map files instead of generated locations. */
    // "inlineSourceMap": true,               /* Emit a single file with source maps instead of having a separate file. */
    // "inlineSources": true,                 /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */

    /* Experimental Options */
    // "experimentalDecorators": true,        /* Enables experimental support for ES7 decorators. */
    // "emitDecoratorMetadata": true,         /* Enables experimental support for emitting type metadata for decorators. */

    /* Advanced Options */
    "forceConsistentCasingInFileNames": true  /* Disallow inconsistently-cased references to the same file. */
  },
  "include": [
    "src/**/*.ts"
  ],
  "exclude": [
    "node_modules",
    "**/*.spec.ts"
  ]
}

3. Main project file: index.ts

This file is relatively simple and is not split into modules.

• Fibonacci numbers can be implemented using recursion or more advanced algebraic methods. For simplicity and demonstration purposes, this project uses the most basic and intuitive loop-based approach.
• In TypeScript, when importing Node's CommonJS modules, it is common to use syntax like import * as readline from 'readline' to keep the coding style consistent.
• The program includes basic error prompts and handling. Non-positive integers will trigger an error message.

import * as readline from 'readline';

// Use readline's createInterface method to create a basic prompt and input/output interface
// Enter quit in the command line to exit the program directly
const rl = readline.createInterface({
  input: process.stdin,
  output: process.stdout,
  prompt: 'Input an int>0,"quit" to exit >'
});

// Basic iterative Fibonacci sequence
const fabonacci = (serial: number): number => {
  let prev1 = 0; // n-1
  let prev2 = 0; // n-1
  let sum = 0;
  for (let i = 1; i <= serial; i++) {
    if (i <= 2) {
      sum = 1;
      prev1 = sum;
      console.log(`i=${i},sum=${sum}`);
    } else if (i > 2) {
      prev2 = prev1;
      prev1 = sum;
      sum = prev1 + prev2;
      console.log(`i=${i},prev1=${prev1},prev2=${prev2},sum=${sum}`);
    }
  }
  return sum;
}

// Distinguish and handle user input
const inputCase = (line: string): string => {
  switch (line.trim()) {
    case 'quit':
      console.log('system shuting down...');
      return 'quit';
    default:
      let lineNumber = parseInt(line);
      if (lineNumber) {
        console.log(`Hello,your input is ${lineNumber}`);
        console.log(`The result is ${fabonacci(lineNumber)}`);
      } else {
        console.log(`Sorry, input invalid,please check again`);
      }
      return 'prompt';
  }
}

// Command prompt and user interface
rl.prompt();
rl.on('line', (line) => {
  let response = inputCase(line);
  if (response === 'quit') {
    rl.close();
  } else if (response === 'prompt') {
    rl.prompt();
  }
})

4. Using the project

Install the project dependencies with npm i (you may also need to install TypeScript globally).

• Enter the project directory