Applied Programming/Conditions/JavaScript

conditions.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

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 {
        let fahrenheit = getFahrenheit();
        let celsius = calculateCelsius(fahrenheit);
        displayResults(fahrenheit, celsius);    
    } catch(error) {
        output("Unexpected error:");
        output(`${error.name}: ${error.message}`);
    }
}

/**
 * Gets Fahrenheit temperature.
 * 
 * @returns {number} Fahrenheit temperature
 * @returns nothing and exits if fahrenheit is not numeric.
 * @returns nothing and exits if fahrenheit is below absolute zero.
 */
function getFahrenheit() {
    let fahrenheit = input("Enter Fahrenheit temperature: ");

    if (isNaN(fahrenheit) || fahrenheit == "") {
        output("Fahrenheit temperature must be a number.");
        output(`TypeError: '${fahrenheit}' is not a number.`);
        process.exit(1)
    }

    fahrenheit = Number(fahrenheit);

    if (fahrenheit < ABSOLUTE_ZERO) {
        output("Fahrenheit temperature cannot be below absolute zero.");
        output(`RangeError: ${fahrenheit} is less than ${ABSOLUTE_ZERO}.`);
        process.exit(2)
    }

    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`);
}

/**
 * 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.
conditions.js

Try It

See Also
