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JScript Cheat Sheet

A quick reference guide for JScript, Microsoft's implementation of ECMAScript, used for Windows scripting. This cheat sheet covers essential syntax, objects, and techniques for automating tasks in Windows environments.

JScript Fundamentals

Basic Syntax

Variables

var variableName = value;
Declares a variable. JScript is loosely typed.

Data Types

Number, String, Boolean, Object, Null, Undefined

Comments

// Single-line comment
/* ... */ Multi-line comment

Operators

Arithmetic (+, -, *, /, %), Assignment (=, +=, -=), Comparison (==, !=, >, <, >=, <=), Logical (&&, ||, !)

Conditional Statements

if (condition) { ... } else { ... }
switch (expression) { case value: ... break; default: ... }

Loops

for (initialization; condition; increment) { ... }
while (condition) { ... }
do { ... } while (condition);

Functions

Function Declaration

function functionName(parameter1, parameter2) { ... return value; }

Function Call

functionName(argument1, argument2);

Anonymous Function

var myFunction = function(parameter) { ... };

Return Statement

return value;
Returns a value from the function.

Arguments Object

Access function arguments using the arguments object.

Working with Objects

Object Creation

Object Literal

var myObject = { property1: value1, property2: value2 };

Constructor Function

 
function MyObject(property1, property2) {
  this.property1 = property1;
  this.property2 = property2;
}
var myObject = new MyObject(value1, value2);

Adding Properties

myObject.newProperty = value;

Accessing Properties

myObject.property1 or myObject["property1"]

Built-in Objects

WScript
Provides methods and properties for interacting with the Windows Script Host.

  • WScript.Echo(message) - Displays a message box.
  • WScript.CreateObject(progID) - Creates an instance of a COM object.
  • WScript.Arguments - Collection of command-line arguments.

FileSystemObject (FSO)
Provides access to the file system.

  • FSO.CreateTextFile(filename, overwrite) - Creates a text file.
  • FSO.OpenTextFile(filename, iomode, create, format) - Opens a text file.
  • FSO.FolderExists(folderpath) - Checks if a folder exists.
  • FSO.FileExists(filepath) - Checks if a file exists.

Shell Object
Provides methods for interacting with the Windows shell.

  • Shell.Run(command, windowStyle, waitOnReturn) - Executes a command.
  • Shell.ExpandEnvironmentStrings(string) - Expands environment variables.
  • Shell.RegWrite(key, value, type) - Writes to the registry.

Advanced JScript Techniques

Error Handling

Try…Catch…Finally

 
try {
  // Code that might throw an error
} catch (error) {
  // Handle the error
  WScript.Echo(error.message);
} finally {
  // Code that executes regardless of error
}

Error Object

The error object in the catch block contains information about the error.

  • error.number - Error code.
  • error.description - Error message.

Working with Arrays

Array Creation

var myArray = [value1, value2, value3]; or var myArray = new Array(value1, value2, value3);

Accessing Elements

myArray[index] (index starts at 0)

Array Methods
  • myArray.push(value) - Adds an element to the end of the array.
  • myArray.pop() - Removes the last element from the array.
  • myArray.length - Returns the number of elements in the array.

Regular Expressions

Creating a RegExp Object

var myRegExp = /pattern/flags; or var myRegExp = new RegExp("pattern", "flags");

RegExp Methods
  • myRegExp.test(string) - Returns true if the string matches the pattern.
  • myRegExp.exec(string) - Returns an array containing the matched text.

Common Flags
  • i - Case-insensitive.
  • g - Global match (find all occurrences).
  • m - Multiline.

JScript and WSH

WSH Scripting

JScript files are executed by the Windows Script Host (WSH). WSH provides a runtime environment for executing scripts written in various scripting languages, including JScript and VBScript.

Scripts are typically saved with a .js extension and can be executed by double-clicking them or by using the wscript.exe or cscript.exe command-line interpreters.

Example Scripts

Displaying a Message Box

WScript.Echo("Hello, World!");

Reading a Text File

var FSO = WScript.CreateObject("Scripting.FileSystemObject");
var file = FSO.OpenTextFile("C:\\example.txt", 1); // 1 = ForReading
var content = file.ReadAll();
file.Close();
WScript.Echo(content);

Creating a Folder

var FSO = WScript.CreateObject("Scripting.FileSystemObject");
var folderPath = "C:\\NewFolder";
if (!FSO.FolderExists(folderPath)) {
  FSO.CreateFolder(folderPath);
  WScript.Echo("Folder created successfully!");
} else {
  WScript.Echo("Folder already exists.");
}

Running an External Program

var Shell = WScript.CreateObject("WScript.Shell");
Shell.Run("notepad.exe");
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