JSON Forgefy 🔧

Transform JSON data with MongoDB-style operators. No database required.

JSON Forgefy lets you reshape, calculate, and transform JSON objects using familiar MongoDB aggregation operators. Perfect for API responses, data pipelines, and any JSON transformation needs.

🎯 What Problems Does It Solve?

• API Response Mapping: Transform external API responses to match your app's data structure
• Data Normalization: Convert inconsistent data formats into standardized schemas
• Calculations: Perform math operations, string manipulations, and conditional logic
• Data Pipelines: Create reusable transformation blueprints for consistent data processing
• Type Safety: Get full TypeScript support with compile-time validation

✨ Key Benefits

• 🚀 Zero Dependencies: Lightweight with no external dependencies
• 📝 Declarative: Define transformations as simple blueprint objects
• 🔄 MongoDB Operators: Use familiar $add, $multiply, $cond, $switch syntax
• 🏗️ Composable: Nest operators and combine transformations seamlessly
• 📦 Type-Safe: Full TypeScript support with comprehensive type definitions
• 🧪 Battle-Tested: 100% test coverage with comprehensive test suite

📦 Installation

pnpm add json-forgefy

# Alternative package managers
npm install json-forgefy
yarn add json-forgefy

🎮 Try It Online

Try JSON Forgefy in your browser with our interactive playground:

• 🌐 Live Playground: https://dmberlin.github.io/json-forgefy-playground
• 📦 Source Code: https://github.com/DMBerlin/json-forgefy-playground

The playground lets you test all 77 operators with real-time transformation, syntax highlighting, and interactive API reference.

🚀 Quick Start

Transform API responses, calculate values, and reshape data in seconds:

import Forgefy from 'json-forgefy';

// Raw API response
const apiResponse = {
  user: { 
    first_name: "john", 
    last_name: "doe", 
    email: "[email protected]",
    balance: "1250.75",
    cpf: "123.456.789-10"
  },
  transaction: { 
    amount: "100.50", 
    currency: "USD",
    status: "pending"
  }
};

// Define your transformation blueprint
const blueprint = {
  // Extract and format user data
  user: {
    fullName: { 
      $concat: [
        { $toUpper: { $substr: { value: "$user.first_name", start: 0, length: 1 } } },
        { $substr: { value: "$user.first_name", start: 1, length: 100 } },
        " ",
        { $toUpper: { $substr: { value: "$user.last_name", start: 0, length: 1 } } },
        { $substr: { value: "$user.last_name", start: 1, length: 100 } }
      ]
    },
    email: "$user.email",
    balance: { $toNumber: "$user.balance" },
    cleanCpf: { 
      $replace: { 
        input: "$user.cpf", 
        searchValues: [".", "-"], 
        replacement: "" 
      } 
    }
  },
  
  // Calculate transaction details
  transaction: {
    amount: { $toNumber: "$transaction.amount" },
    amountCents: { $multiply: [{ $toNumber: "$transaction.amount" }, 100] },
    currency: "$transaction.currency",
    status: { $toUpper: "$transaction.status" },
    isHighValue: { $gt: [{ $toNumber: "$transaction.amount" }, 100] }
  }
};

// Transform the data
const result = Forgefy.this(apiResponse, blueprint);

// Output:
{
  user: {
    fullName: "John Doe",
    email: "[email protected]", 
    balance: 1250.75,
    cleanCpf: "12345678910"
  },
  transaction: {
    amount: 100.5,
    amountCents: 10050,
    currency: "USD",
    status: "PENDING",
    isHighValue: true
  }
}

💼 Real-World Use Cases

1. API Response Standardization

Transform inconsistent third-party API responses into your app's data structure:

// External API returns snake_case, you need camelCase
const externalApiData = {
  user_id: 123,
  first_name: "jane",
  account_balance: "2500.00",
  is_premium_member: true
};

const blueprint = {
  id: "$user_id",
  firstName: "$first_name", 
  balance: { $toNumber: "$account_balance" },
  isPremium: "$is_premium_member",
  tier: {
    $cond: {
      if: "$is_premium_member",
      then: "Premium",
      else: "Standard"
    }
  }
};

// Transform the data
const result = Forgefy.this(externalApiData, blueprint);

// Output:
{
  id: 123,
  firstName: "jane",
  balance: 2500,
  isPremium: true,
  tier: "Premium"
}

2. Financial Calculations

Process payment data with complex calculations:

const paymentData = {
  subtotal: "99.99",
  tax_rate: "0.08",
  discount_percent: "10",
  shipping: "5.99"
};

const blueprint = {
  subtotal: { $toNumber: "$subtotal" },
  tax: { 
    $multiply: [
      { $toNumber: "$subtotal" }, 
      { $toNumber: "$tax_rate" }
    ] 
  },
  discount: {
    $multiply: [
      { $toNumber: "$subtotal" },
      { $divide: [{ $toNumber: "$discount_percent" }, 100] }
    ]
  },
  total: {
    $add: [
      { $toNumber: "$subtotal" },
      { $multiply: [{ $toNumber: "$subtotal" }, { $toNumber: "$tax_rate" }] },
      { $toNumber: "$shipping" },
      { $multiply: [
        { $toNumber: "$subtotal" },
        { $divide: [{ $toNumber: "$discount_percent" }, 100] }
      ]}
    ]
  }
};

// Transform the data
const result = Forgefy.this(paymentData, blueprint);

// Output:
{
  subtotal: 99.99,
  tax: 8.00,
  discount: 10.00,
  total: 123.99
}

3. Data Validation & Conditional Logic

Apply business rules and validation:

const userData = {
  age: 25,
  country: "US",
  subscription_type: "premium",
  last_login: "2024-01-15T10:30:00Z"
};

const blueprint = {
  canAccessPremium: {
    $and: [
      { $gte: ["$age", 18] },
      { $eq: ["$subscription_type", "premium"] }
    ]
  },
  region: {
    $switch: {
      branches: [
        { case: { $eq: ["$country", "US"] }, then: "North America" },
        { case: { $eq: ["$country", "CA"] }, then: "North America" },
        { case: { $eq: ["$country", "GB"] }, then: "Europe" }
      ],
      default: "Other"
    }
  },
  accountStatus: {
    $cond: {
      if: { $gt: [{ $dateDiff: { startDate: "$last_login", endDate: "now", unit: "days" } }, 30] },
      then: "Inactive",
      else: "Active"
    }
  }
};

// Transform the data
const result = Forgefy.this(userData, blueprint);

// Output:
{
  canAccessPremium: true,
  region: "North America", 
  accountStatus: "Inactive"
}

🔧 Core Concepts

1. Path Extraction

Use $ prefix to extract values from nested objects:

const data = { user: { profile: { name: "Alice" } } };
const blueprint = { name: "$user.profile.name" };
// Transform the data
const result = Forgefy.this(data, blueprint);
// Result: { name: "Alice" }

2. Operators

Transform data using MongoDB-style operators:

const blueprint = {
  total: { $add: [10, 20, 30] },           // Math operations
  text: { $toString: 123 },                // Type conversions
  upper: { $toUpper: "$user.name" },       // String operations
  conditional: {                           // Conditional logic
    $cond: {
      if: { $gt: ["$amount", 100] },
      then: "Premium",
      else: "Standard"
    }
  }
};

3. Nested Transformations

Create complex nested structures:

const blueprint = {
  user: {
    id: "$userId",
    profile: {
      displayName: { $toUpper: "$user.name" },
      isActive: { $eq: ["$status", "active"] }
    }
  },
  summary: {
    total: { $add: ["$price", "$tax"] },
    formatted: { $concat: ["$", { $toString: { $add: ["$price", "$tax"] } }] }
  }
};

📚 Complete Operator Reference

📖 For detailed API documentation with comprehensive examples, see GUIDE.md

77 operators across 10 categories:

| Category | Operators | Count | |----------|-----------|-------| | 🔢 Mathematical | $add, $subtract, $multiply, $divide, $abs, $ceil, $floor, $max, $min, $toFixed, $round, $mod, $pow, $sqrt, $trunc | 15 | | 📝 String | $concat, $toUpper, $toLower, $substr, $slice, $split, $size, $replace, $regexReplace, $trim, $ltrim, $rtrim, $indexOf, $replaceOne, $replaceAll | 15 | | ⚖️ Comparison | $eq, $ne, $gt, $gte, $lt, $lte, $in, $nin, $regex | 9 | | 🔀 Logical | $and, $or, $not, $none | 4 | | 🎯 Conditional | $cond, $switch, $ifNull, $coalesce, $every, $some | 6 | | 🔄 Type Conversion | $toNumber, $toString, $toDate | 3 | | 🔍 Type Checking | $type, $isArray, $isString, $isBoolean, $isDate, $isNumber, $isNull, $isNaN, $exists | 9 | | 📅 Date | $dayOfWeek, $dayOfMonth, $dayOfYear, $isWeekend, $isHoliday, $addDays, $dateShift, $dateDiff | 8 | | 📋 Array Transform | $map, $filter, $reduce | 3 | | 📊 Array Utilities | $arrayFirst, $arrayLast, $arrayAt, $sum, $avg | 5 |

🔢 Mathematical Operations

Perfect for calculations, aggregations, and numeric transformations:

| Operator | Description | Example | Result | |----------|-------------|---------|---------| | $add | Add numbers | { $add: [1, 2, 3] } | 6 | | $subtract | Subtract numbers | { $subtract: [10, 3] } | 7 | | $multiply | Multiply numbers | { $multiply: [4, 5] } | 20 | | $divide | Divide numbers | { $divide: [20, 4] } | 5 | | $abs | Absolute value | { $abs: -5 } | 5 | | $ceil | Round up | { $ceil: 4.2 } | 5 | | $floor | Round down | { $floor: 4.8 } | 4 | | $max | Maximum value | { $max: [1, 5, 3] } | 5 | | $min | Minimum value | { $min: [1, 5, 3] } | 1 | | $toFixed | Format decimals | { $toFixed: { value: 3.14159, precision: 2 } } | 3.14 | | $round | Round to precision | { $round: { value: 3.14159, precision: 2 } } | 3.14 | | $mod | Modulo (remainder) | { $mod: { dividend: 10, divisor: 3 } } | 1 | | $pow | Power/exponentiation | { $pow: { base: 2, exponent: 3 } } | 8 | | $sqrt | Square root | { $sqrt: { value: 16 } } | 4 | | $trunc | Truncate to integer | { $trunc: 4.9 } | 4 |

// Basic arithmetic
const math = {
  sum: { $add: [10, 20, 30] },                    // 60
  difference: { $subtract: [100, 25] },            // 75
  product: { $multiply: [5, 6] },                  // 30
  quotient: { $divide: [100, 4] },                 // 25
  absolute: { $abs: -42 },                         // 42
  roundUp: { $ceil: 4.2 },                         // 5
  roundDown: { $floor: 4.8 },                      // 4
  maximum: { $max: [10, 25, 15] },                 // 25
  minimum: { $min: [10, 25, 15] }                  // 10
};

// Advanced math
const advanced = {
  remainder: { $mod: { dividend: 17, divisor: 5 } },      // 2
  power: { $pow: { base: 2, exponent: 10 } },             // 1024
  squareRoot: { $sqrt: { value: 144 } },                  // 12
  truncated: { $trunc: 3.9 },                             // 3
  formatted: { $toFixed: { value: 3.14159, precision: 2 } }, // "3.14"
  rounded: { $round: { value: 3.14159, precision: 2 } }   // 3.14
};

// With fallback for errors
const safe = {
  safeSqrt: { $sqrt: { value: -16, fallback: 0 } }        // 0 (negative number)
};

📝 String Operations

Transform and manipulate text data:

| Operator | Description | Example | Result | |----------|-------------|---------|---------| | $toString | Convert to string | { $toString: 123 } | "123" | | $toUpper | Uppercase | { $toUpper: "hello" } | "HELLO" | | $toLower | Lowercase | { $toLower: "HELLO" } | "hello" | | $concat | Join strings | { $concat: ["Hello", " ", "World"] } | "Hello World" | | $substr | Extract substring | { $substr: { value: "Hello", start: 1, length: 3 } } | "ell" | | $slice | Slice string/array | { $slice: { input: "Hello", start: 0, end: 2 } } | "He" | | $split | Split string | { $split: { input: "a,b,c", delimiter: "," } } | ["a", "b", "c"] | | $size | Get length | { $size: "Hello" } | 5 | | $replace | Replace multiple values | { $replace: { input: "123.456.789-10", searchValues: [".", "-"], replacement: "" } } | "12345678910" | | $regexReplace | Regex replacement | { $regexReplace: { input: "hello world", pattern: "\\s+", replacement: " " } } | "hello world" | | $trim | Trim whitespace/chars | { $trim: { input: " hello ", chars: [" "] } } | "hello" | | $ltrim | Trim left | { $ltrim: { input: " hello", chars: [" "] } } | "hello" | | $rtrim | Trim right | { $rtrim: { input: "hello ", chars: [" "] } } | "hello" | | $indexOf | Find substring index | { $indexOf: { input: "hello", substring: "ll" } } | 2 | | $replaceOne | Replace first match | { $replaceOne: { input: "hello", search: "l", replacement: "L" } } | "heLlo" | | $replaceAll | Replace all matches | { $replaceAll: { input: "hello", search: "l", replacement: "L" } } | "heLLo" |

// Basic string operations
const strings = {
  upper: { $toUpper: "hello world" },                     // "HELLO WORLD"
  lower: { $toLower: "HELLO WORLD" },                     // "hello world"
  joined: { $concat: ["Hello", " ", "World", "!"] },      // "Hello World!"
  substring: { $substr: { value: "Hello World", start: 6, length: 5 } }, // "World"
  sliced: { $slice: { input: "Hello", start: 1, end: 4 } }, // "ell"
  parts: { $split: { input: "a,b,c", delimiter: "," } },  // ["a", "b", "c"]
  length: { $size: "Hello" }                              // 5
};

// Advanced string manipulation
const advanced = {
  cleaned: { $trim: { input: "  hello  ", chars: [" "] } },              // "hello"
  leftTrim: { $ltrim: { input: "  hello", chars: [" "] } },             // "hello"
  rightTrim: { $rtrim: { input: "hello  ", chars: [" "] } },            // "hello"
  position: { $indexOf: { input: "hello world", substring: "world" } }, // 6
  replaceFirst: { $replaceOne: { input: "hello", search: "l", replacement: "L" } }, // "heLlo"
  replaceAll: { $replaceAll: { input: "hello", search: "l", replacement: "L" } }    // "heLLo"
};

// Pattern replacement
const patterns = {
  // Remove all non-digits
  digitsOnly: { 
    $regexReplace: { input: "ABC-123-XYZ", pattern: "\\D", replacement: "" } 
  },  // "123"
  
  // Normalize whitespace
  normalized: { 
    $regexReplace: { input: "hello    world", pattern: "\\s+", replacement: " " } 
  },  // "hello world"
  
  // Clean phone number
  cleanPhone: { 
    $replace: { 
      input: "(555) 123-4567", 
      searchValues: ["(", ")", " ", "-"], 
      replacement: "" 
    } 
  }  // "5551234567"
};

⚖️ Comparison & Logic

Make decisions and validate data:

| Operator | Description | Example | Result | |----------|-------------|---------|---------| | $eq | Equal | { $eq: [5, 5] } | true | | $ne | Not equal | { $ne: [5, 3] } | true | | $gt | Greater than | { $gt: [10, 5] } | true | | $gte | Greater or equal | { $gte: [5, 5] } | true | | $lt | Less than | { $lt: [3, 5] } | true | | $lte | Less or equal | { $lte: [5, 5] } | true | | $and | Logical AND | { $and: [true, false] } | false | | $or | Logical OR | { $or: [true, false] } | true | | $not | Logical NOT | { $not: true } | false | | $none | All conditions false | { $none: [false, false] } | true | | $in | Value in array | { $in: ["a", ["a", "b"]] } | true | | $nin | Value not in array | { $nin: ["c", ["a", "b"]] } | true | | $exists | Field exists | { $exists: "$field" } | true/false | | $isNull | Is null/undefined | { $isNull: null } | true | | $isNumber | Is valid number | { $isNumber: 123 } | true | | $isNaN | Is NaN | { $isNaN: NaN } | true | | $regex | Pattern matching | { $regex: { value: "$email", pattern: "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}$" } } | true/false |

// Comparisons
const checks = {
  isEqual: { $eq: [5, 5] },                        // true
  notEqual: { $ne: [5, 3] },                       // true
  greaterThan: { $gt: [10, 5] },                   // true
  greaterOrEqual: { $gte: [5, 5] },                // true
  lessThan: { $lt: [3, 5] },                       // true
  lessOrEqual: { $lte: [5, 5] }                    // true
};

// Logical operators
const logic = {
  allTrue: { $and: [true, true, true] },           // true
  anyTrue: { $or: [false, true, false] },          // true
  inverted: { $not: false },                       // true
  noneTrue: { $none: [false, false, false] }       // true
};

// Membership
const membership = {
  inList: { $in: ["apple", ["apple", "banana"]] }, // true
  notInList: { $nin: ["grape", ["apple", "banana"]] } // true
};

// Validation
const validation = {
  hasField: { $exists: "$user.email" },            // true/false
  isNull: { $isNull: "$optionalField" },           // true/false
  isValidNumber: { $isNumber: "$age" },            // true/false
  isNotANumber: { $isNaN: "$invalidNumber" }       // true/false
};

// Pattern matching
const patterns = {
  isEmail: { 
    $regex: { 
      value: "$email", 
      pattern: "^[^@]+@[^@]+\\.[^@]+$" 
    } 
  }  // true/false
};

🔀 Conditional Logic

Handle complex decision-making:

| Operator | Description | Example | |----------|-------------|---------| | $cond | If-then-else | { $cond: { if: { $gt: ["$age", 18] }, then: "Adult", else: "Minor" } } | | $switch | Multi-branch | { $switch: { branches: [{ case: { $eq: ["$type", "A"] }, then: "Type A" }], default: "Other" } } | | $ifNull | Null coalescing | { $ifNull: ["$optional", "default"] } | | $coalesce | First non-null value | { $coalesce: ["$displayName", "$firstName", "Anonymous"] } | | $every | All conditions true | { $every: { conditions: [...], then: "valid", else: "invalid" } } | | $some | Any condition true | { $some: { conditions: [...], then: "found", else: "none" } } |

// If-then-else with $cond
const status = {
  age: 25,
  category: {
    $cond: {
      if: { $gte: ["$age", 18] },
      then: "Adult",
      else: "Minor"
    }
  }  // "Adult"
};

// Multi-branch with $switch
const tier = {
  score: 850,
  level: {
    $switch: {
      branches: [
        { case: { $gte: ["$score", 900] }, then: "Platinum" },
        { case: { $gte: ["$score", 800] }, then: "Gold" },
        { case: { $gte: ["$score", 700] }, then: "Silver" }
      ],
      default: "Bronze"
    }
  }  // "Gold"
};

// Null handling
const safe = {
  optionalName: null,
  displayName: { $coalesce: ["$optionalName", "$firstName", "Guest"] }, // Uses first non-null
  safeName: { $ifNull: ["$optionalName", "Unknown"] }                   // "Unknown"
};

// Multiple conditions
const validation = {
  checks: [
    { $gte: ["$age", 18] },
    { $eq: ["$status", "active"] },
    "$verified"
  ],
  allValid: { $every: { conditions: "$checks", then: true, else: false } },
  anyValid: { $some: { conditions: "$checks", then: true, else: false } }
};

🔄 Type Conversion

Convert between data types safely:

| Operator | Description | Example | Result | |----------|-------------|---------|---------| | $toNumber | Convert to number | { $toNumber: "123" } | 123 | | $toString | Convert to string | { $toString: 123 } | "123" |

// Number conversion
const numbers = {
  fromString: { $toNumber: "123.45" },             // 123.45
  fromBoolean: { $toNumber: true },                // 1
  invalid: { $toNumber: "abc" }                    // NaN
};

// String conversion
const strings = {
  fromNumber: { $toString: 123 },                  // "123"
  fromBoolean: { $toString: true },                // "true"
  fromNull: { $toString: null }                    // "null"
};

📅 Date Operations

Work with dates, extract components, and handle business days:

| Operator | Description | Example | Result | |----------|-------------|---------|---------| | $toDate | Convert to date | { $toDate: { date: "2025-01-15" } } | Date object | | $dayOfWeek | Day of week (0-6) | { $dayOfWeek: { date: "$date" } } | 0-6 | | $dayOfMonth | Day of month (1-31) | { $dayOfMonth: { date: "$date" } } | 1-31 | | $dayOfYear | Day of year (1-366) | { $dayOfYear: { date: "$date" } } | 1-366 | | $isWeekend | Check if weekend | { $isWeekend: { date: "$date" } } | true/false | | $isHoliday | Check if holiday | { $isHoliday: { date: "$date", holidays: ["2025-01-01"] } } | true/false | | $addDays | Add/subtract days | { $addDays: { date: "$date", days: 7 } } | "2025-01-22" | | $dateShift | Shift to business day | { $dateShift: { date: "$date", strategy: "rollForward", holidays: "$holidays" } } | "2025-01-20" | | $dateDiff | Calculate difference | { $dateDiff: { startDate: "$start", endDate: "$end", unit: "days" } } | 10 |

// Extract date components
const dateInfo = {
  date: "2025-03-15T10:00:00Z",
  dayOfWeek: { $dayOfWeek: { date: "$date" } },        // 6 (Saturday)
  dayOfMonth: { $dayOfMonth: { date: "$date" } },      // 15
  dayOfYear: { $dayOfYear: { date: "$date" } },        // 74
  isWeekend: { $isWeekend: { date: "$date" } }         // true
};

// Business day handling
const businessDay = {
  scheduledDate: "2025-03-01",  // Saturday
  holidays: ["2025-03-03"],     // Monday is holiday
  executionDate: {
    $dateShift: {
      date: "$scheduledDate",
      strategy: "rollForward",    // Options: rollForward, rollBackward, keep
      holidays: "$holidays",
      weekends: [6, 0]           // Saturday, Sunday
    }
  }
  // Result: "2025-03-04" (Tuesday - skips weekend and holiday)
};

// Date arithmetic
const futureDate = {
  today: "2025-01-01",
  nextWeek: { $addDays: { date: "$today", days: 7 } },      // "2025-01-08"
  lastMonth: { $addDays: { date: "$today", days: -30 } }    // "2024-12-02"
};

📋 Array Transformation

Transform, filter, and aggregate arrays:

| Operator | Description | Example | |----------|-------------|---------| | $map | Transform each element | { $map: { input: "$items", expression: { $multiply: ["$current", 2] } } } | | $filter | Filter elements | { $filter: { input: "$items", condition: { $gt: ["$current", 10] } } } | | $reduce | Aggregate to single value | { $reduce: { input: "$items", initialValue: 0, expression: { $add: ["$accumulated", "$current"] } } } |

// Transform array elements with $map
const doubled = {
  numbers: [1, 2, 3, 4, 5],
  doubled: {
    $map: {
      input: "$numbers",
      expression: { $multiply: ["$current", 2] }
    }
  }
  // Result: [2, 4, 6, 8, 10]
};

// Filter array with conditions
const adults = {
  users: [
    { name: "Alice", age: 25 },
    { name: "Bob", age: 17 },
    { name: "Charlie", age: 30 }
  ],
  adults: {
    $filter: {
      input: "$users",
      condition: { $gte: ["$current.age", 18] }
    }
  }
  // Result: [{ name: "Alice", age: 25 }, { name: "Charlie", age: 30 }]
};

// Aggregate with $reduce
const sum = {
  values: [1, 2, 3, 4, 5],
  total: {
    $reduce: {
      input: "$values",
      initialValue: 0,
      expression: { $add: ["$accumulated", "$current"] }
    }
  }
  // Result: 15
};

// Context variables in array operators
// $current - current element
// $index - current index (0-based)
// $accumulated - accumulated value (in $reduce)

📊 Array Utilities

Access and aggregate array elements:

| Operator | Description | Example | Result | |----------|-------------|---------|---------| | $arrayFirst | First element | { $arrayFirst: { input: [1, 2, 3] } } | 1 | | $arrayLast | Last element | { $arrayLast: { input: [1, 2, 3] } } | 3 | | $arrayAt | Element at index | { $arrayAt: { input: [1, 2, 3], index: 1 } } | 2 | | $sum | Sum numbers | { $sum: { values: [1, 2, 3] } } | 6 | | $avg | Average | { $avg: { values: [1, 2, 3] } } | 2 |

// Access specific elements
const scores = {
  all: [85, 92, 78, 95, 88],
  first: { $arrayFirst: { input: "$all" } },          // 85
  last: { $arrayLast: { input: "$all" } },            // 88
  third: { $arrayAt: { input: "$all", index: 2 } },   // 78
  secondLast: { $arrayAt: { input: "$all", index: -2 } }  // 95 (negative indexing)
};

// Aggregate numbers
const stats = {
  values: [10, 20, 30, 40, 50],
  total: { $sum: { values: "$values" } },             // 150
  average: { $avg: { values: "$values" } },           // 30
  count: { $size: "$values" }                         // 5
};

// With fallback for safety
const safe = {
  maybeArray: null,
  first: { 
    $arrayFirst: { 
      input: "$maybeArray", 
      fallback: "default" 
    } 
  }  // "default"
};

🔍 Type Checking

Validate data types:

| Operator | Description | Example | Result | |----------|-------------|---------|---------| | $type | Get type name | { $type: "$value" } | "string" | | $isArray | Check if array | { $isArray: "$value" } | true/false | | $isString | Check if string | { $isString: "$value" } | true/false | | $isBoolean | Check if boolean | { $isBoolean: "$value" } | true/false | | $isDate | Check if valid date | { $isDate: "$value" } | true/false |

// Type identification
const types = {
  stringType: { $type: "hello" },                  // "string"
  numberType: { $type: 123 },                      // "number"
  arrayType: { $type: [1, 2, 3] },                 // "array"
  objectType: { $type: { a: 1 } },                 // "object"
  nullType: { $type: null },                       // "null"
  undefinedType: { $type: undefined }              // "undefined"
};

// Type validation
const checks = {
  checkArray: { $isArray: [1, 2, 3] },             // true
  checkString: { $isString: "hello" },             // true
  checkBoolean: { $isBoolean: true },              // true
  checkDate: { $isDate: "2025-01-01" }             // true
};

// Use in conditionals
const conditional = {
  value: [1, 2, 3],
  result: {
    $cond: {
      if: { $isArray: "$value" },
      then: { $size: "$value" },
      else: 0
    }
  }  // 3
};

🎯 Common Patterns & Best Practices

Pattern 1: Data Normalization

Standardize inconsistent API responses:

// Transform snake_case API to camelCase
const normalizeUser = {
  userId: "$user_id",
  firstName: "$first_name", 
  lastName: "$last_name",
  emailAddress: "$email_address",
  accountBalance: { $toNumber: "$account_balance" },
  isVerified: "$is_verified",
  createdAt: "$created_at"
};

Pattern 2: Calculated Fields

Add computed properties to your data:

const addCalculations = {
  // Keep original data
  price: "$price",
  tax: "$tax",
  
  // Add calculated fields
  subtotal: { $add: ["$price", "$tax"] },
  discountAmount: { $multiply: ["$price", "$discountRate"] },
  finalPrice: { 
    $subtract: [
      { $add: ["$price", "$tax"] },
      { $multiply: ["$price", "$discountRate"] }
    ]
  },
  isExpensive: { $gt: ["$price", 100] }
};

Pattern 3: Conditional Data Enrichment

Add fields based on business logic:

const enrichUserData = {
  // Basic user info
  name: "$name",
  age: "$age",
  
  // Conditional enrichment
  category: {
    $switch: {
      branches: [
        { case: { $lt: ["$age", 18] }, then: "Minor" },
        { case: { $lt: ["$age", 65] }, then: "Adult" }
      ],
      default: "Senior"
    }
  },
  canVote: { $gte: ["$age", 18] },
  greeting: {
    $cond: {
      if: { $gte: ["$age", 18] },
      then: { $concat: ["Hello ", "$name", ", you can vote!"] },
      else: { $concat: ["Hi ", "$name", ", you'll be able to vote in ", { $toString: { $subtract: [18, "$age"] } }, " years"] }
    }
  }
};

Pattern 4: Data Validation & Sanitization

Clean and validate incoming data:

const validateAndClean = {
  // Clean string data
  email: { $toLower: "$email" },
  // Clean CPF by removing dots and dashes
  cleanCpf: { 
    $replace: { 
      input: "$cpf", 
      searchValues: [".", "-"], 
      replacement: "" 
    } 
  },
  name: { 
    $concat: [
      { $toUpper: { $substr: { value: "$firstName", start: 0, length: 1 } } },
      { $substr: { value: "$firstName", start: 1, length: 100 } },
      " ",
      { $toUpper: { $substr: { value: "$lastName", start: 0, length: 1 } } },
      { $substr: { value: "$lastName", start: 1, length: 100 } }
    ]
  },
  
  // Validate and set defaults
  age: { $ifNull: ["$age", 0] },
  isValidEmail: { $regex: { value: "$email", pattern: "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}$" } },
  status: {
    $cond: {
      if: { $and: ["$email", { $gt: ["$age", 0] }] },
      then: "Valid",
      else: "Invalid"
    }
  }
};

Pattern 5: Advanced Text Processing with RegexReplace

Use regex patterns for complex string transformations:

const textProcessing = {
  // Normalize whitespace - handle any number of spaces
  normalizedText: {
    $trim: {
      input: {
        $regexReplace: {
          input: "$userInput",              // "  hello      world  "
          pattern: "\\s+",                   // Match one or more whitespace chars
          replacement: " "
        }
      }
    }
  },  // Result: "hello world"
  
  // Clean phone number - remove all non-digits
  cleanPhone: {
    $regexReplace: {
      input: "$phone",                      // "(555) 123-4567"
      pattern: "\\D",                       // Match any non-digit
      replacement: ""
    }
  },  // Result: "5551234567"
  
  // Remove HTML tags
  plainText: {
    $regexReplace: {
      input: "$htmlContent",                // "<p>Hello <strong>World</strong></p>"
      pattern: "<[^>]+>",                   // Match HTML tags
      replacement: ""
    }
  },  // Result: "Hello World"
  
  // Case-insensitive replacement
  sanitized: {
    $regexReplace: {
      input: "$text",                       // "Test TEST test"
      pattern: "test",
      replacement: "demo",
      flags: "gi"                           // Global + case-insensitive
    }
  },  // Result: "demo demo demo"
  
  // Combine with other operators for validation
  hasValidPhone: {
    $eq: [
      {
        $size: {
          $regexReplace: {
            input: "$phone",
            pattern: "\\D",
            replacement: ""
          }
        }
      },
      10
    ]
  }  // Check if phone has exactly 10 digits
};

🛡️ Fallback System

Many operators support fallback values for graceful error handling:

// Array operators with fallback
const safe = {
  maybeArray: null,
  
  // Returns fallback if input is not an array
  first: { 
    $arrayFirst: { 
      input: "$maybeArray", 
      fallback: "no data" 
    } 
  },  // "no data"
  
  // Math operators with fallback
  safeSqrt: { 
    $sqrt: { 
      value: "$negativeNumber", 
      fallback: 0 
    } 
  },  // 0 (if negative)
  
  // Sum with fallback for non-numeric values
  total: { 
    $sum: { 
      values: ["$invalidData"], 
      fallback: 0 
    } 
  }  // 0
};

// Fallback can be:
// - Static value: fallback: 0
// - Path reference: fallback: "$defaultValue"
// - Expression: fallback: { $add: [1, 2] }

📌 Important Notes

Array Operator Limitations

Due to JavaScript module circular dependencies, array operators ($map, $filter, $reduce) cannot be nested within object properties:

// ❌ This doesn't work (nested $map in object property)
{
  $map: {
    input: [{ items: [1, 2, 3] }],
    expression: {
      doubled: {  // ← Nested in object property
        $map: { input: "$current.items", expression: { $multiply: ["$current", 2] } }
      }
    }
  }
}
// Returns: [{ doubled: null }]

// ✅ Use $map at expression root instead
{
  $map: {
    input: [{ items: [1, 2, 3] }],
    expression: {
      $map: {  // ← At root level
        input: "$current.items",
        expression: { $multiply: ["$current", 2] }
      }
    }
  }
}
// Returns: [[2, 4, 6]]

All other operators nest perfectly to unlimited depth.

🛠️ Development

Prerequisites

• Node.js 16+
• pnpm (recommended) or npm/yarn

Setup

# Clone the repository
git clone https://github.com/DMBerlin/json-forgefy.git
cd json-forgefy

# Install dependencies with pnpm
pnpm install

# Run tests
pnpm test

# Build the project
pnpm build

# Run linting
pnpm lint

Development Commands

# Run all tests
pnpm test

# Run tests in watch mode
pnpm test:watch

# Run tests with coverage
pnpm test:cov

# Lint and fix code
pnpm lint:fix

# Build for production
pnpm build

📖 API Reference

Forgefy.this(payload, projection)

The main transformation function.

Parameters:

• payload (Record<string, any>): The source object to transform
• projection (Projection): The blueprint object defining the transformation

Returns:

• Record<string, any>: The transformed object

Example:

const result = Forgefy.this(sourceData, transformationBlueprint);

🤝 Contributing

We welcome contributions! Please see our Contributing Guidelines for details.

1. Fork the repository
2. Create your feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'Add some amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request

📝 License

This project is licensed under the ISC License - see the LICENSE file for details.

🙏 Acknowledgments

• Inspired by MongoDB's aggregation pipeline operators
• Built with TypeScript for type safety and developer experience
• Designed for modern JavaScript/TypeScript applications

Made with ❤️ by Daniel Marinho