JS Built-ins
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ArrayArray.prototype.concatbeginner

Array.prototype.concat() — join multiple arrays

📖 Usage Example
const a = [1]
const b = [2, 3]
const c = [4, 5]
a.concat(b, c)  // → [1, 2, 3, 4, 5]

Pass multiple arrays to concat() to join them all in a single call.

Array.prototype.concat() — multiple arguments

concat() can accept multiple arrays as arguments, joining them all in one call.

Challenge: Implement joinAll(arrays) that concatenates an array of number arrays into a single flat array.

joinAll([[1, 2], [3, 4], [5]]) // → [1, 2, 3, 4, 5]
joinAll([[1], [], [2]])        // → [1, 2]
💡 Hints (2)
  • • Use spread syntax: `[].concat(...arrays)` to spread the array of arrays as individual arguments.
  • • Alternatively, `arrays.reduce((acc, arr) => acc.concat(arr), [])` works too.