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FunctionalProgrammingintermediate

Pure vs impure — array operations

📖 Usage Example
// Pure: returns new array
const pureAdd = (arr, item) => [...arr, item];
// Impure: mutates original
const impureAdd = (arr, item) => { arr.push(item); };

Pure functions avoid mutating arguments — return new values instead.

Distinguishing Pure and Impure Functions

Learn to identify pure functions by checking whether they modify their inputs or depend on external state.

Challenge: Create a pure version of array transformation. Given an array, return a new array with each element doubled without modifying the original.

💡 Hints (3)
  • • Use .map() to create a new array
  • • Never modify the input array
  • • Pure functions should not have side effects