Description

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Beginner · 9 min

Spread and rest

Copy a collection and collect an unknown number of arguments.

Copy and extend

Spread syntax expands an array into another array. For objects, it copies own enumerable properties. These copies are shallow: nested objects remain shared.

const original = ["Read", "Practice"];
const updated = [...original, "Review"];
console.log(original.length);
console.log(updated.join(", "));

Output

2
Read, Practice, Review

Collect arguments

A rest parameter gathers remaining arguments into an array. It must be the last parameter.

function total(...values) {
  return values.reduce((sum, value) => sum + value, 0);
}
console.log(total(2, 3, 4));

Output

9

Put it into practice

  1. Predict each result before running the example.
  2. Complete the coding task, then explain why your solution works.

Try it yourself

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Extend without mutation

Create updated by copying tasks and adding "Review". Keep tasks unchanged and display both lengths.

Practice