ES6 object destructuring with a default value assignment

Question

Consider the following code:

const log = ({a,b=a}) => console.log(a,b);
log({a:\'a\'})

The variable b is assigned the value

Answer 1

Am I allowed to do this kind of default value assignment in a destructured object?

Yes. The destructuring expression is evaluated from left to right, and you can use variables that are already initialised from properties in the default initialiser expressions of later properties.

Remember that it desugars to

const log = (o) => {
  var a = o.a;
  var b = o.b !== undefined ? o.b : a;
//                                  ^ a is usable here
  console.log(a,b);
};