Developer Tools Quick Reference

Encoding & Decoding

Base64 Encoding

Purpose: Convert binary data to ASCII text Use cases: Email attachments, data URLs, API tokens

Example:

Text: "Hello World"
Base64: "SGVsbG8gV29ybGQ="

Data URL Example:

data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8/5+hHgAHggJ/PchI7wAAAABJRU5ErkJggg==

URL Encoding (Percent Encoding)

Purpose: Encode special characters in URLs Format: %XX (hexadecimal)

| Character | Encoded | Description | |-----------|---------|-------------| | Space | %20 | Space character | | ! | %21 | Exclamation mark | | " | %22 | Quotation mark | | # | %23 | Hash/pound | | $ | %24 | Dollar sign | | % | %25 | Percent sign | | & | %26 | Ampersand | | + | %2B | Plus sign | | ? | %3F | Question mark |

Example:

Original: "Hello World & More!"
Encoded:  "Hello%20World%20%26%20More%21"

HTML Entity Encoding

| Character | Entity | Numeric | |-----------|--------|---------| | < | < | < | | > | > | > | | & | & | & | | " | " | " | | ' | ' | ' |

Hash Functions

MD5 (Message Digest 5)

Output: 128-bit (32 hex characters)
Security: Broken, not for passwords
Use: File integrity, checksums
Example: "hello" → "5d41402abc4b2a76b9719d911017c592"

SHA-1 (Secure Hash Algorithm 1)

Output: 160-bit (40 hex characters)
Security: Deprecated for security
Use: Legacy systems, Git commits
Example: "hello" → "aaf4c61ddcc5e8a2dabede0f3b482cd9aea9434d"

SHA-256

Output: 256-bit (64 hex characters)
Security: Currently secure
Use: Passwords (with salt), certificates
Example: "hello" → "2cf24dba4f21d4288094e9b9eb4e5f164359294e"

Hash Security Guidelines

Never use MD5 or SHA-1 for passwords
Always use salt with password hashes
Use bcrypt, scrypt, or Argon2 for passwords
SHA-256+ acceptable for data integrity

JSON (JavaScript Object Notation)

Basic Structure

{
  "string": "value",
  "number": 42,
  "boolean": true,
  "null": null,
  "array": [1, 2, 3],
  "object": {
    "nested": "value"
  }
}

Data Types

String: "text" (double quotes required)
Number: 42, 3.14, -17, 1.2e-3
Boolean: true, false
null: null
Array: [1, 2, 3]
Object: {"key": "value"}

Common JSON Operations

// Parse JSON string
const obj = JSON.parse('{"name": "John"}');

// Convert to JSON string
const json = JSON.stringify({name: "John"});

// Pretty print (formatted)
const formatted = JSON.stringify(obj, null, 2);

JSON Validation Rules

✅ Double quotes for strings
✅ No trailing commas
✅ No comments allowed
❌ Single quotes: 'invalid'
❌ Trailing comma: {"a": 1,}
❌ Comments: // not allowed

UUID (Universally Unique Identifier)

UUID Versions

UUID v1: Timestamp + MAC address
UUID v4: Random (most common)
UUID v5: Namespace + name (SHA-1)

UUID v4 Format

xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx
Example: 550e8400-e29b-41d4-a716-446655440000

Use Cases

Database primary keys
Session identifiers
File names
API request IDs

Regular Expressions (Regex)

Common Patterns

Email: ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$
Phone: ^\+?[1-9]\d{1,14}$
URL: ^https?:\/\/(www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()@:%_\+.~#?&//=]*)$
IP Address: ^(?:[0-9]{1,3}\.){3}[0-9]{1,3}$

Regex Modifiers

g: Global (find all matches)
i: Case insensitive
m: Multiline
s: Dot matches newline

HTTP Status Codes

Success (2xx)

200: OK
201: Created
204: No Content

Redirection (3xx)

301: Moved Permanently
302: Found (Temporary Redirect)
304: Not Modified

Client Error (4xx)

400: Bad Request
401: Unauthorized
403: Forbidden
404: Not Found
429: Too Many Requests

Server Error (5xx)

500: Internal Server Error
502: Bad Gateway
503: Service Unavailable

Timestamp Formats

Unix Timestamp

Format: Seconds since January 1, 1970 UTC
Example: 1640995200 = 2022-01-01 00:00:00 UTC

ISO 8601

Format: YYYY-MM-DDTHH:mm:ss.sssZ
Example: 2022-01-01T00:00:00.000Z

Conversion Formulas

// Unix to Date
const date = new Date(timestamp * 1000);

// Date to Unix
const timestamp = Math.floor(date.getTime() / 1000);

// Current Unix timestamp
const now = Math.floor(Date.now() / 1000);

Color Codes

Hex Colors

#RRGGBB format
#FF0000 = Red
#00FF00 = Green
#0000FF = Blue
#FFFFFF = White
#000000 = Black

RGB/RGBA

rgb(255, 0, 0)     /* Red */
rgba(255, 0, 0, 0.5) /* Semi-transparent red */

HSL/HSLA

hsl(0, 100%, 50%)     /* Red */
hsla(0, 100%, 50%, 0.5) /* Semi-transparent red */

Quick Reference Commands

Git

git status          # Check status
git add .           # Stage all changes
git commit -m "msg" # Commit with message
git push            # Push to remote
git pull            # Pull from remote

npm/Node.js

npm init            # Initialize project
npm install package # Install package
npm run script     # Run script
node file.js       # Run JavaScript file

Note: Advanced topics like JWT tokens, OAuth flows, and API design patterns will be added soon.

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