Introduction to COBOL.js

COBOL.js is a modern JavaScript-based interpreter for the COBOL programming language. It brings the power and reliability of COBOL to web browsers and Node.js environments.

Why COBOL.js?

COBOL remains one of the most important programming languages in enterprise computing. COBOL.js makes it accessible to modern developers while maintaining compatibility with traditional COBOL syntax.

Your First COBOL Program

IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO-WORLD.
PROCEDURE DIVISION.
    DISPLAY "Hello, COBOL.js World!".
    STOP RUN.

The example above demonstrates a basic COBOL program structure. Click the Run Example button to execute it and see the output in the panel on the right.

Installation

Getting started with COBOL.js is straightforward. You can use it in the browser or install it via npm for Node.js projects.

Browser Usage

Include the COBOL.js library in your HTML file:

HTML Setup

IDENTIFICATION DIVISION.
PROGRAM-ID. SETUP-DEMO.
DATA DIVISION.
    WORKING-STORAGE SECTION.
    01 WS-MESSAGE PIC X(30) VALUE "COBOL.js is ready!".
PROCEDURE DIVISION.
    DISPLAY WS-MESSAGE.
    STOP RUN.

Node.js Installation

For Node.js projects, install COBOL.js via npm:

npm install cobol.js

Quick Start Guide

This guide will help you write and run your first COBOL.js program in minutes.

Basic Program Structure

Every COBOL program follows a standard structure with four main divisions:

Complete Program Example

IDENTIFICATION DIVISION.
PROGRAM-ID. QUICK-START.
DATA DIVISION.
    WORKING-STORAGE SECTION.
    01 WS-NAME PIC X(20).
    01 WS-AGE PIC 99.
PROCEDURE DIVISION.
    MOVE "John Doe" TO WS-NAME.
    MOVE 25 TO WS-AGE.
    DISPLAY "Name: " WS-NAME.
    DISPLAY "Age: " WS-AGE.
    STOP RUN.

Program Structure

COBOL programs are organized into four main divisions, each serving a specific purpose.

The Four Divisions

Understanding the division structure is crucial for writing effective COBOL programs.

Division Structure

IDENTIFICATION DIVISION.
PROGRAM-ID. DIVISION-DEMO.
AUTHOR. COBOL.JS TEAM.
DATE-WRITTEN. 2025.

ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
SOURCE-COMPUTER. COBOL-JS.
OBJECT-COMPUTER. BROWSER.

DATA DIVISION.
    WORKING-STORAGE SECTION.
    01 WS-COUNTER PIC 9(3) VALUE 0.
    01 WS-MESSAGE PIC X(50).

PROCEDURE DIVISION.
    PERFORM VARYING WS-COUNTER FROM 1 BY 1 UNTIL WS-COUNTER > 3
        STRING "Iteration " WS-COUNTER INTO WS-MESSAGE
        DISPLAY WS-MESSAGE
    END-PERFORM.
    STOP RUN.

Understanding Divisions

Each division in COBOL serves a specific purpose in program organization.

Identification Division

Contains program identification and documentation information.

Identification Division Example

IDENTIFICATION DIVISION.
PROGRAM-ID. PAYROLL-SYSTEM.
AUTHOR. DEVELOPMENT TEAM.
DATE-WRITTEN. 2025-07-15.
REMARKS. This program processes employee payroll.

PROCEDURE DIVISION.
    DISPLAY "Program: PAYROLL-SYSTEM".
    DISPLAY "Version: 1.0".
    DISPLAY "Status: Ready for processing".
    STOP RUN.

Data Division

The most important division for defining data structures and variables.

Data Division Example

IDENTIFICATION DIVISION.
PROGRAM-ID. DATA-DEMO.
DATA DIVISION.
    WORKING-STORAGE SECTION.
    01 EMPLOYEE-RECORD.
        05 EMP-ID PIC 9(5).
        05 EMP-NAME PIC X(30).
        05 EMP-SALARY PIC 9(6)V99.
    01 WS-TOTAL-SALARY PIC 9(8)V99 VALUE 0.
    
PROCEDURE DIVISION.
    MOVE 12345 TO EMP-ID.
    MOVE "Alice Johnson" TO EMP-NAME.
    MOVE 75000.50 TO EMP-SALARY.
    
    DISPLAY "Employee ID: " EMP-ID.
    DISPLAY "Employee Name: " EMP-NAME.
    DISPLAY "Employee Salary: " EMP-SALARY.
    STOP RUN.

Data Types

COBOL uses picture clauses (PIC) to define data types and formats.

Common Picture Clauses

Understanding PIC clauses is essential for COBOL data manipulation.

Data Types Example

IDENTIFICATION DIVISION.
PROGRAM-ID. DATA-TYPES.
DATA DIVISION.
    WORKING-STORAGE SECTION.
    01 WS-INTEGER PIC 9(5) VALUE 12345.
    01 WS-DECIMAL PIC 9(5)V99 VALUE 123.45.
    01 WS-STRING PIC X(20) VALUE "Hello COBOL".
    01 WS-SIGNED PIC S9(4) VALUE -999.
    01 WS-ALPHA PIC A(10) VALUE "ALPHABET".
    
PROCEDURE DIVISION.
    DISPLAY "Integer: " WS-INTEGER.
    DISPLAY "Decimal: " WS-DECIMAL.
    DISPLAY "String: " WS-STRING.
    DISPLAY "Signed: " WS-SIGNED.
    DISPLAY "Alpha: " WS-ALPHA.
    STOP RUN.

Working with Variables

Variables in COBOL are defined in the DATA DIVISION and manipulated in the PROCEDURE DIVISION.

Variable Operations

Learn how to declare, initialize, and manipulate variables effectively.

Variable Operations

IDENTIFICATION DIVISION.
PROGRAM-ID. VARIABLES.
DATA DIVISION.
    WORKING-STORAGE SECTION.
    01 WS-NUM1 PIC 9(3) VALUE 100.
    01 WS-NUM2 PIC 9(3) VALUE 200.
    01 WS-RESULT PIC 9(4).
    01 WS-NAME PIC X(15) VALUE "COBOL".
    01 WS-FULL-NAME PIC X(30).
    
PROCEDURE DIVISION.
    ADD WS-NUM1 TO WS-NUM2 GIVING WS-RESULT.
    DISPLAY "Sum: " WS-RESULT.
    
    STRING WS-NAME " Programming" INTO WS-FULL-NAME.
    DISPLAY "Full Name: " WS-FULL-NAME.
    
    MOVE 42 TO WS-NUM1.
    DISPLAY "Updated NUM1: " WS-NUM1.
    STOP RUN.

Arithmetic Operations

COBOL provides comprehensive arithmetic operations for numerical computations.

Basic Arithmetic

Master the fundamental arithmetic operations in COBOL.

Arithmetic Example

IDENTIFICATION DIVISION.
PROGRAM-ID. ARITHMETIC.
DATA DIVISION.
    WORKING-STORAGE SECTION.
    01 WS-NUM1 PIC 9(3) VALUE 50.
    01 WS-NUM2 PIC 9(3) VALUE 25.
    01 WS-RESULT PIC 9(4).
    01 WS-REMAINDER PIC 9(3).
    
PROCEDURE DIVISION.
    ADD WS-NUM1 TO WS-NUM2 GIVING WS-RESULT.
    DISPLAY "Addition: " WS-NUM1 " + " WS-NUM2 " = " WS-RESULT.
    
    SUBTRACT WS-NUM2 FROM WS-NUM1 GIVING WS-RESULT.
    DISPLAY "Subtraction: " WS-NUM1 " - " WS-NUM2 " = " WS-RESULT.
    
    MULTIPLY WS-NUM1 BY WS-NUM2 GIVING WS-RESULT.
    DISPLAY "Multiplication: " WS-NUM1 " * " WS-NUM2 " = " WS-RESULT.
    
    DIVIDE WS-NUM1 BY WS-NUM2 GIVING WS-RESULT REMAINDER WS-REMAINDER.
    DISPLAY "Division: " WS-NUM1 " / " WS-NUM2 " = " WS-RESULT " remainder " WS-REMAINDER.
    STOP RUN.

String Handling

COBOL provides powerful string manipulation capabilities for text processing.

String Operations

Learn to concatenate, inspect, and manipulate strings effectively.

String Handling Example

IDENTIFICATION DIVISION.
PROGRAM-ID. STRING-HANDLING.
DATA DIVISION.
    WORKING-STORAGE SECTION.
    01 WS-FIRST-NAME PIC X(10) VALUE "John".
    01 WS-LAST-NAME PIC X(10) VALUE "Smith".
    01 WS-FULL-NAME PIC X(25).
    01 WS-UPPER-NAME PIC X(25).
    01 WS-LENGTH PIC 99.
    
PROCEDURE DIVISION.
    STRING WS-FIRST-NAME " " WS-LAST-NAME INTO WS-FULL-NAME.
    DISPLAY "Full Name: " WS-FULL-NAME.
    
    MOVE FUNCTION UPPER-CASE(WS-FULL-NAME) TO WS-UPPER-NAME.
    DISPLAY "Upper Case: " WS-UPPER-NAME.
    
    MOVE FUNCTION LENGTH(WS-FULL-NAME) TO WS-LENGTH.
    DISPLAY "Length: " WS-LENGTH.
    
    INSPECT WS-FULL-NAME REPLACING ALL "John" BY "Jane".
    DISPLAY "Modified: " WS-FULL-NAME.
    STOP RUN.

Control Flow

COBOL provides various control structures for program flow management.

Conditional Statements and Loops

Master IF statements, PERFORM loops, and other control structures.

Control Flow Example

IDENTIFICATION DIVISION.
PROGRAM-ID. CONTROL-FLOW.
DATA DIVISION.
    WORKING-STORAGE SECTION.
    01 WS-COUNTER PIC 9(2) VALUE 1.
    01 WS-GRADE PIC 9(3) VALUE 85.
    01 WS-STATUS PIC X(10).
    
PROCEDURE DIVISION.
    IF WS-GRADE >= 90
        MOVE "Excellent" TO WS-STATUS
    ELSE IF WS-GRADE >= 80
        MOVE "Good" TO WS-STATUS
    ELSE IF WS-GRADE >= 70
        MOVE "Average" TO WS-STATUS
    ELSE
        MOVE "Poor" TO WS-STATUS
    END-IF.
    
    DISPLAY "Grade: " WS-GRADE " Status: " WS-STATUS.
    
    DISPLAY "Counting from 1 to 5:".
    PERFORM VARYING WS-COUNTER FROM 1 BY 1 UNTIL WS-COUNTER > 5
        DISPLAY "Count: " WS-COUNTER
    END-PERFORM.
    STOP RUN.

File Handling

COBOL excels at file processing operations, a cornerstone of business computing.

File Operations

Learn to read, write, and process files in COBOL applications.

File Handling Concepts

IDENTIFICATION DIVISION.
PROGRAM-ID. FILE-DEMO.
DATA DIVISION.
    WORKING-STORAGE SECTION.
    01 WS-EMPLOYEE-RECORD.
        05 WS-EMP-ID PIC 9(5).
        05 WS-EMP-NAME PIC X(20).
        05 WS-EMP-DEPT PIC X(10).
    01 WS-RECORD-COUNT PIC 9(3) VALUE 0.
    
PROCEDURE DIVISION.
    DISPLAY "File Processing Demo".
    DISPLAY "=====================".
    
    MOVE 10001 TO WS-EMP-ID.
    MOVE "Alice Johnson" TO WS-EMP-NAME.
    MOVE "IT" TO WS-EMP-DEPT.
    ADD 1 TO WS-RECORD-COUNT.
    DISPLAY "Record " WS-RECORD-COUNT ": " WS-EMP-ID " " WS-EMP-NAME " " WS-EMP-DEPT.
    
    MOVE 10002 TO WS-EMP-ID.
    MOVE "Bob Smith" TO WS-EMP-NAME.
    MOVE "HR" TO WS-EMP-DEPT.
    ADD 1 TO WS-RECORD-COUNT.
    DISPLAY "Record " WS-RECORD-COUNT ": " WS-EMP-ID " " WS-EMP-NAME " " WS-EMP-DEPT.
    
    DISPLAY "Total records processed: " WS-RECORD-COUNT.
    STOP RUN.

Subroutines and Paragraphs

Organize your code with subroutines and paragraphs for better maintainability.

PERFORM Statements

Use PERFORM to execute paragraphs and create reusable code blocks.

Subroutines Example

IDENTIFICATION DIVISION.
PROGRAM-ID. SUBROUTINES.
DATA DIVISION.
    WORKING-STORAGE SECTION.
    01 WS-NUM1 PIC 9(3) VALUE 15.
    01 WS-NUM2 PIC 9(3) VALUE 25.
    01 WS-RESULT PIC 9(4).
    
PROCEDURE DIVISION.
    DISPLAY "Subroutine Demo".
    DISPLAY "===============".
    
    PERFORM CALCULATE-SUM.
    PERFORM CALCULATE-PRODUCT.
    PERFORM DISPLAY-RESULTS.
    
    STOP RUN.

CALCULATE-SUM.
    ADD WS-NUM1 TO WS-NUM2 GIVING WS-RESULT.
    DISPLAY "Sum calculated: " WS-RESULT.

CALCULATE-PRODUCT.
    MULTIPLY WS-NUM1 BY WS-NUM2 GIVING WS-RESULT.
    DISPLAY "Product calculated: " WS-RESULT.

DISPLAY-RESULTS.
    DISPLAY "Processing completed successfully".
    DISPLAY "Thank you for using COBOL.js".

Debugging Techniques

Learn effective debugging strategies for COBOL.js applications.

Debug Output and Error Handling

Use DISPLAY statements and error handling to debug your programs.

Debugging Example

IDENTIFICATION DIVISION.
PROGRAM-ID. DEBUG-DEMO.
DATA DIVISION.
    WORKING-STORAGE SECTION.
    01 WS-DIVIDEND PIC 9(3) VALUE 100.
    01 WS-DIVISOR PIC 9(3) VALUE 5.
    01 WS-RESULT PIC 9(4).
    01 WS-DEBUG-FLAG PIC X VALUE "Y".
    
PROCEDURE DIVISION.
    IF WS-DEBUG-FLAG = "Y"
        DISPLAY "DEBUG: Starting division operation"
        DISPLAY "DEBUG: Dividend = " WS-DIVIDEND
        DISPLAY "DEBUG: Divisor = " WS-DIVISOR
    END-IF.
    
    IF WS-DIVISOR = 0
        DISPLAY "ERROR: Division by zero detected!"
        DISPLAY "ERROR: Program terminated"
        STOP RUN
    END-IF.
    
    DIVIDE WS-DIVIDEND BY WS-DIVISOR GIVING WS-RESULT.
    
    IF WS-DEBUG-FLAG = "Y"
        DISPLAY "DEBUG: Division completed successfully"
        DISPLAY "DEBUG: Result = " WS-RESULT
    END-IF.
    
    DISPLAY "Final result: " WS-DIVIDEND " / " WS-DIVISOR " = " WS-RESULT.
    STOP RUN.

Introduction to COBOL.js

Why COBOL.js?

Installation

Browser Usage

Node.js Installation

Quick Start Guide

Basic Program Structure

Program Structure

The Four Divisions

Understanding Divisions

Identification Division

Data Division

Data Types

Common Picture Clauses

Working with Variables

Variable Operations

Arithmetic Operations

Basic Arithmetic

String Handling

String Operations

Control Flow

Conditional Statements and Loops

File Handling

File Operations

Subroutines and Paragraphs

PERFORM Statements

Debugging Techniques

Debug Output and Error Handling

Output Console