Default and Rest Parameters

Revisit defaults and rest on function expressions and arrows.

Phase 10 §58 introduced defaults and rest on classic functions. Here the same ideas appear on expressions and arrows, with a few more call patterns.

Default (arrow)

Rest after a named param

Default in the middle

Results appear here.

Try each demo.

Important JavaScript

const heading = (title = "Untitled") => {
  return "# " + title;
};

const totalWithBonuses = function (base, ...bonuses) {
  let sum = base;
  bonuses.forEach(function (n) {
    sum = sum + n;
  });
  return sum;
};

const multiply = (left, right = 1) => left * right;

heading();                 // "# Untitled"
heading("Practice");       // "# Practice"
totalWithBonuses(10, 5, 3);
multiply(4);               // 4 * 1 → 4
multiply(4, 3);            // 12