Default value on object parameter

// destructuring with default value
function someFunction({ a = 1 } = {}) {
  // a does not exist in the object, always defaults to 1
  console.log(a);
}

someFunction(); // 1

OR

const value = fetchValue(); // can be undefined

const obj = {
  variables: {
    value: value || 1 // default value is 1
  }
};

function someFunction(obj) {
  console.log(obj.variables.value);
}

someFunction(obj); // 1

Caveat

You cant do this:

const value = fetchValue(); // can be undefined

function someFunction({ variables: { value: value || 1 } }) {
  console.log(obj.variables.value);
}

When you pass a literal structure in the argument, it will be parsed as a destructuring assignment and will cause syntax error when handling a default value with a || operator.

What is arguments keyword

Array-like object accessible inside functions that contain the values of the arguments passed to that function.

function someFunction(a, b, c) {
  console.log(arguments);
}

someFunction(1, 2, 3); // { 0: 1, 1: 2, 2: 3 }