编程基础/字符串示例 JavaScript

字符串

 // 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)}`);
 } 
 
 function output(text) {
   if (typeof document === 'object') {
     document.write(text);
   } 
   else if (typeof console === 'object') {
     console.log(text);
   } 
   else {
     print(text);
   }
 }

输出

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

文件

注意：出于安全原因，浏览器中的 JavaScript 需要用户选择要处理的文件。本示例基于 node.js 而不是基于浏览器的 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();

输出

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

参考资料

• 维基教科书: 计算机编程

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