Recursion

1. What is Recursive Function?

• A function that calls itself

• When recursion is suitable to use

  • When a given problem can be divided into smaller problems with similar structure

  • When there are many nested loops or when it's difficult to predict the number of nested loops

• Example code

  // Conditional statement that returns 0 when an empty array is received
  // Code that solves the smallest problem & code that stops recursion
  function arrSum(arr) {
    if (arr.length === 0) {
      return 0;
    }
    // First element of array + arrSum function that receives array with remaining elements
    // Code that breaks down the problem through recursion
    // arrSum([5]) === 5 + arrSum([]) === 5 + 0 === 5;
    // arrSum([4, 5]) === 4 + arrSum([5]) === 4 + 5 === 9;
    return arr.shift() + arrSum(arr);
  }

2. Recursive Thinking

1. Define the input and output of the recursive function

• Define in the most abstract or simplest way

2. Break down the problem and divide into cases

• Break down according to input values or problem order/size

3. Solve simple problems

• Solve the easiest problem first → recursion base: this constitutes the escape condition for future recursion

• If there's no escape condition, the recursive function calls itself endlessly, so break down the problem as small as possible

4. Solve complex problems

• Solve the remaining complex problems

5. Implement the code

function recursive (input1, input2, ...) {
    // base case: when the problem can no longer be broken down
    if (when the problem can no longer be broken down) {
        return answer to the simple problem;
    }

    // recursive case: otherwise
    return problem newly defined as a smaller problem
}

3.JSON.stringigy

1. Background of JSON Creation

• JSON is JavaScript Object Notation, an object format created for data exchange between different programs

2. Methods

JSON.stringify: Method to convert object → JSON

// Method JSON.stringify to convert message object to JSON

let transferableMessage = JSON.stringify(message);

console.log(transferableMessage);
// `{"sender":"Ella","receiver":"Chloe","message":"Hi, Chloe.","createdAt":"2023-04-12 10:10:10"}`

console.log(typeof transferableMessage); // `string`

JSON.parse: Method to convert JSON → object

// Apply JSON.parse method to serialized JSON to convert back to object: deserialization

let packet = `{"sender":"Ella","receiver":"Chloe","message":"Hi, Chloe.","createdAt":"2023-04-12 10:10:10"}`;
let obj = JSON.parse(packet);

console.log(obj);
/*
 * {
 * sender: "Ella",
 * receiver: "Chloe",
 * message: "Hi, Chloe.",
 * createdAt: "2023-04-12 10:10:10"
 * }
 */

console.log(typeof obj); // `object`

3. JSON Basic Rules

json_rules.png