Applied Programming/Files/JavaScript

files.js

/* This program demonstrates synchronous file I/O. It creates a file, 
displays the file, appends data to the file, displays the file, and
then deletes the file. It will not run if the file already exists.

Input:
    None

Output:
    C       F
    0       32.0
    1       33.8
    ...

References:
    https://www.geeksforgeeks.org/node-js-fs-readfile-method/
    https://www.geeksforgeeks.org/node-js-fs-writefilesync-method/
    https://flaviocopes.com/how-to-remove-file-node/
*/

const fs = require("fs");

if (typeof module != "undefined" && !module.parent) {
    main();
}

/**
  * Runs the main program logic.
  */
function main()
{
    var filename = "~file.txt";

    if(fileExists(filename))
    {
        console.log("File already exists.")
    }
    else
    {
        createFile(filename);
        readFile(filename);
        appendFile(filename);
        readFile(filename);
        deleteFile(filename);
    }
}

/**
 * Creates a text file.
 * 
 * @param Text filename to create.
 */
function createFile(filename)
{
    let data = "C\tF\n";
    for(let celsius = 0; celsius <= 50; celsius++)
    {
        let fahrenheit = celsius * 9 / 5 + 32;
        data += `${celsius}\t${fahrenheit.toFixed(1)}\n`;
    }

    try {
        fs.writeFileSync(filename, data);
    } catch (error) {
        console.error(error);
    }
}

/**
 * Reads a text file.
 * 
 * @param Text filename to read.
 */
function readFile(filename)
{
    try {
        let data = fs.readFileSync(filename, "utf-8");
        let lines = data.split("\n");
        for(const line of lines) {
            console.log(line);
        }
    } catch (error) {
        console.error(error);
    }
}

/**
 * Append to a text file.
 * 
 * @param Text filename to append to.
 */
function appendFile(filename)
{
    let data = "";
    for(let celsius = 51; celsius <= 100; celsius++)
    {
        let fahrenheit = celsius * 9 / 5 + 32;
        data += `${celsius}\t${fahrenheit.toFixed(1)}\n`;
    }

    try {
        fs.appendFileSync(filename, data);
    } catch (error) {
        console.error(error);
    }
}

/**
 * Deletes a file.
 * 
 * @param Text filename to delete.
 */
function deleteFile(filename)
{
    try {
        fs.unlinkSync(filename);
    } catch (error) {
        console.error(error);
    }
}

/**
 * Checks to see if a file exists.
 * 
 * @param Text filename to check.
 * @returns true if exists or false if not.
 */
function fileExists(filename)
{
    return fs.existsSync(filename);
}
Try It

Copy and paste the code above into one of the following free online development environments or use your own JavaScript compiler / interpreter / IDE.
files.js

Try It

See Also
