Prompt Title: Complex REST API Design.

The spread operator in JavaScript is denoted by three dots .... It is a powerful feature introduced in ECMAScript 6 (ES6) that allows you to expand elements from an iterable (like an array or a string) into individual elements. The spread operator is used in various contexts to simplify certain operations and make code more concise and readable.

Here are some common use cases of the spread operator:

1. Array Spreading: The spread operator can be used to create a new array by copying the elements of an existing array or combining multiple arrays into one.

   javascriptCopy code
   const array1 = [1, 2, 3];
   const array2 = [4, 5, 6];
   
   // Create a new array by copying elements from array1
   const newArray1 = [...array1]; // [1, 2, 3]
   
   // Combine multiple arrays into one
   const combinedArray = [...array1, ...array2]; // [1, 2, 3, 4, 5, 6]
   

2. Function Arguments: The spread operator can be used in function arguments to pass an array as individual arguments to a function.

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   function sum(a, b, c) {
     return a + b + c;
   }
   
   const numbers = [1, 2, 3];
   const result = sum(...numbers); // Equivalent to sum(1, 2, 3)
   console.log(result); // 6
   

3. Object Spreading (ES9+): The spread operator can also be used to create a shallow copy of an object or merge multiple objects into one.

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   const obj1 = { x: 1, y: 2 };
   const obj2 = { z: 3 };
   
   // Create a shallow copy of an object
   const newObj1 = { ...obj1 }; // { x: 1, y: 2 }
   
   // Merge multiple objects into one
   const mergedObj = { ...obj1, ...obj2 }; // { x: 1, y: 2, z: 3 }
   

4. String Spreading (ES9+): The spread operator can be used to convert a string into an array of characters.

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   const str = "Hello";
   const charArray = [...str]; // ['H', 'e', 'l', 'l', 'o']
   

5. Function Rest Parameters: The spread operator can also be used as part of function declarations to capture multiple arguments into an array (rest parameters).

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   function printArgs(...args) {
     console.log(args);
   }
   
   printArgs(1, 2, 3); // [1, 2, 3]
   

Please note that the spread operator creates shallow copies. That means if you have nested arrays or objects, only the top-level elements are copied, and the nested elements will still reference the same objects. To achieve a deep copy, you need to use more advanced techniques like JSON.parse(JSON.stringify(obj)) or utility libraries like lodash.cloneDeep().