Applied Programming/Loops/JavaScript

loops.js

/* This program converts a Fahrenheit temperature to Celsius.

Input:
    Fahrenheit temperature

Output:
    Fahrenheit temperature
    Celsius temperature

Example:
    Enter Fahrenheit temperature: 100
    100° Fahrenheit is 37.77777777777778° Celsius

    ...
    
    Enter Fahrenheit temperature or press <Enter> to quit: 

References:
    * http://sphinxcontrib-napoleon.readthedocs.io/en/latest/example_google.html
    * https://javascript.info/comments
    * http://www.mathsisfun.com/temperature-conversion.html
    * https://nodejs.org/api/process.html#processexitcode
    * https://javascript.info/try-catch
    * https://javascript.info/types
*/

const TEMPERATURE_DIFFERENCE = 32;
const TEMPERATURE_RATIO = 5 / 9;
const ABSOLUTE_ZERO = -459.67;

main();

/**
 * Runs main program logic.
 */
function main() {
    try {
        while (true) {
            let fahrenheit = getFahrenheit();
            if (fahrenheit === "") {
                break;
            }
            let celsius = calculateCelsius(fahrenheit);
            displayResults(fahrenheit, celsius);
            displayTable(fahrenheit);
        }
    } catch (error) {
        output("Unexpected error:");
        output(`${error.name}: ${error.message}`);
    }
}

/**
 * Gets Fahrenheit temperature.
 * 
 * @returns {number} Fahrenheit temperature or empty string
 */
function getFahrenheit() {
    while (true) {
        let fahrenheit = input("Enter Fahrenheit temperature or press <Enter> to quit: ");
        if (fahrenheit === "") {
            return fahrenheit;
        }

        if (isNaN(fahrenheit)) {
            output("Fahrenheit temperature must be a number.");
            output(`TypeError: '${fahrenheit}' is not a number.`);
            continue;
        }
    
        fahrenheit = Number(fahrenheit);
    
        if (fahrenheit < ABSOLUTE_ZERO) {
            output("Fahrenheit temperature cannot be below absolute zero.");
            output(`RangeError: ${fahrenheit} is less than ${ABSOLUTE_ZERO}.`);
            continue;
        }

        return fahrenheit;
    }
}

/**
 * Converts Fahrenheit temperature to Celsius.
 * 
 * @param {number} Fahrenheit temperature
 * @returns {number} Celsius temperature
 * @throws TypeError if fahrenheit is not numeric.
 * @throws RangeError if fahrenheit is below absolute zero.
 */
function calculateCelsius(fahrenheit) {
    if (typeof fahrenheit != "number") {
        throw(new TypeError(`'${fahrenheit}' is not a number.`))
    }

    if (fahrenheit < ABSOLUTE_ZERO) {
        throw(new RangeError(`'${fahrenheit}' is below absolute zero.`))
    }

    let celsius = (fahrenheit - TEMPERATURE_DIFFERENCE) * TEMPERATURE_RATIO;
    return celsius;
}

/**
 * Displays Fahrenheit and Celsius temperatures.
 * 
 * @param {number} Fahrenheit temperature
 * @param {number} Celsius temperature
 */
function displayResults(fahrenheit, celsius) {
    console.assert(typeof fahrenheit == "number");
    console.assert(typeof celsius == "number");

    output(`${fahrenheit}° Fahrenheit is ${celsius}° Celsius`);
}

/**
 * Displays nearest multiples of 10 Fahrenheit and Celsius temperatures.
 * 
 * @param {number} Fahrenheit temperature
 */
function displayTable(fahrenheit) {
    console.assert(typeof fahrenheit == "number");

    output("");
    output("F\tC")
    let start = Math.floor(fahrenheit / 10) * 10
    for (let fahrenheit = start; fahrenheit < start + 11; fahrenheit++) {
        let celsius = calculateCelsius(fahrenheit);
        output(`${fahrenheit.toFixed(1)}\t${celsius.toFixed(1)}`)
    }
    output("");
}

/**
 * Generic input function to get input in HTML, Node, or Rhino environments.
 * 
 * @param {string} text prompt
 * @returns {string} input
 */
function input(text) {
    if (typeof window === 'object') {
        return prompt(text)
    }
    else if (typeof console === 'object') {
        const rls = require('readline-sync');
        let value = rls.question(text);
        return value;
    }
    else {
        output(text);
        let isr = new java.io.InputStreamReader(java.lang.System.in);
        let br = new java.io.BufferedReader(isr);
        let line = br.readLine();
        return line.trim();
    }
}

/**
 * Generic output function to display output in HTML, Node, or Rhino environments.
 * 
 * @param {string} text prompt
 * @returns {string} input
 */
function output(text) {
    if (typeof document === 'object') {
        document.write(text);
    }
    else if (typeof console === 'object') {
        console.log(text);
    }
    else {
        print(text);
    }
}
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.
loops.js

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See Also
