27.8.4: JavaScript Examples
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Strings
// This program demonstrates string functions. main(); function main() { var str = "Hello"; output("string: " + str); output("string.toLowerCase(): " + str.toLowerCase()); output("string.toUpperCase(): " + str.toUpperCase()); output("string.indexOf('e'): " + str.indexOf('e')); output("string.length: " + str.length); output("string.replace('H', 'j'): " + str.replace('H', 'j')); output("string(substring(2,4): " + str.substring(2, 4)); output("string.trim(): " + str.trim()); var name = "Bob"; var value = 123.456; output(`string.format(): ${name} earned $${value.toFixed(2)}`); } // Checks the JavaScript environment and writes to the console, // the current document, or standard output as appropriate. // Reference: http://progopedia.com/example/hello-world/114/ function output(text) { if (typeof console === "object") { console.log(text); } else if (typeof document === "object") { document.write(text); } else { print(text); } }
Output
string: Hello string..toLowerCase(): hello string.toUpperCase(): HELLO string.indexOf('e'): 1 string.length: 5 string.replace('H', 'j'): jello string(substring(2,4): ll string.trim(): Hello string.format(): Bob earned $123.46
Files
Note: For security reasons, JavaScript in a browser requires the user to select the file to be processed. This example is based on node.js rather than browser-based JavaScript.
// This program creates a file, adds data to the file, displays the file, // appends more data to the file, displays the file, and then deletes the file. // It will not run if the file already exists. function calculateFahrenheit(celsius) { fahrenheit = celsius * 9 / 5 + 32 return fahrenheit } function createFile(filename) { var fs = require('fs') fs.writeFile(filename, "Celsius,Fahrenheit\n", function(err) { if (err) return console.error(err); }); for(var celsius = 0; celsius <= 50; celsius++) { var fahrenheit = calculateFahrenheit(celsius); fs.appendFile(filename, celsius.toFixed(1) + "," + fahrenheit.toFixed(1) + "\n", function (err) { if (err) { return console.error(err); } }); } } function readFile(filename) { var file = require('readline').createInterface( { input: require('fs').createReadStream(filename) }); file.on('line', function (line) { console.log(line); }); } function appendFile(filename) { var fs = require('fs') for(var celsius = 51; celsius <= 100; celsius++) { var fahrenheit = calculateFahrenheit(celsius); fs.appendFile(filename, celsius.toFixed(1) + "," + fahrenheit.toFixed(1) + "\n", function (err) { if (err) { return console.error(err); } }); } } function deleteFile(filename) { var fs = require("fs"); fs.unlink(filename, function(err) { if (err) { return console.error(err); } }); } function fileExists(filename) { var fs = require('fs'); return fs.existsSync(filename); } 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); } } main();
Output
Celsius,Fahrenheit 0.0,32.0 1.0,33.8 2.0,35.6 ... 98.0,208.4 99.0,210.2 100.0,212.0
References
- Wikiversity: Computer Programming