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routes/lesson6.js

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// This program reads a user-selected text file of countries
// and Celsius temperatures. It displays the data in Celsius
// and Fahrenheit sorted in descending order by temperature.
//
// File format:
// Country,MaximumTemperature
// Bulgaria,45.2 °C
// Canada,45 °C
//
//  https://www.mathsisfun.com/temperature-conversion.html
//  https://en.wikibooks.org/wiki/JavaScript
//  https://www.npmjs.com/package/express-fileupload

const express = require('express')
const fs = require("fs");
const handlebars = require('handlebars');
const router = express.Router()

router.get("/", function (request, response) {
    let source = fs.readFileSync("./templates/lesson6.html");
    let template = handlebars.compile(source.toString());
    let data = {
        table: ""
    }
    result = template(data);
    response.send(result);
});

router.post("/", function (request, response) {
    let result = "";

    if (!request.files || Object.keys(request.files).length == 0) {
        result = "No file selected"
    } else {
        let file = request.files.file;
        result += "<h2>" + file.name + "</h2>";
        result += processFile(file)
    }

    let source = fs.readFileSync("./templates/lesson6.html");
    let template = handlebars.compile(source.toString());
    let data = {
        table: result
    }
    result = template(data);
    response.send(result);
});

function processFile(file) {
    let text = file.data.toString();
    let lines = text.trim().split("\n");
    if (lines[0].toLowerCase().indexOf("country") >= 0) {
        // remove heading line
        lines.shift();
    }

    let table = [];
    for (let index = 0; index < lines.length; index++) {
        try {
            let array = processLine(lines[index]);
            table.push(array);
        }
        catch(error) {
            return error;
        }
    }

    table.sort(function(a, b) {return b[1] - a[1]});
    result = formatTable(table);
    return result
}

function processLine(line) {
    let array = line.split(",");
    if (array.length != 2) {
        throw "Invalid file format"
    }

    let celsius = array[1];
    let index = celsius.indexOf(" °C");
    if (index < 0) {
        throw "Invalid file format";
    }

    celsius = Number(celsius.substring(0, index));
    array[1] = celsius;
    let fahrenheit = celsius * 9 / 5 + 32;
    array.push(fahrenheit)
    return array;
}

function formatTable(table) {
    let result = "<table><tr><th>Country</th>"
    result += "<th>Celsius</th>";
    result += "<th>Fahrenheit</th></tr>";

    for (index = 0; index < table.length; index++) {
        let row = table[index];
        result += "<tr><td>" + row[0] + "</td>";
        result += "<td>" + row[1].toFixed(1) + "° C</td>";
        result += "<td>" + row[2].toFixed(1) + "° F</td></tr>";        
    }

    result += "</table>";
    return result;
}

module.exports = router;

templates/lesson6.html

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<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>Lesson 6</title>
    <link rel="stylesheet" href="styles.css">
    <style>
        p {
            min-height: 1em;
        }
    </style>
</head>

<body>
    <h1>Temperature Conversion</h1>
    <p>Select a file of Celsius temperatures for conversion:</p>
    <form method="POST" enctype="multipart/form-data">
        <input type="file" id="file" name="file">
        <input type="submit">
    </form>
    {{{table}}}
</body>

</html>

Try It

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See Server-Side Scripting/Routes and Templates/Node.js (Express) to create a test environment.

See Server-Side Scripting/Strings and Files/Node.js (Express) for app.js content.

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