i got two noob questions about destructure an array:
1st question: when destructuring an object, I can define a new value or a new key or both. On array, can I add a new value without add a new key?
const obj = {a: undefined, b:2};
const {a = 3, b} = obj;
console.log(a); // 3
I want to know if there is a version of this but with array instead.
2nd question: is it possible to do not provide a default value for objects? Considering that I think that it is not possible to change default values using destructure.
const obj = [1, {a: 1, b:2}, 3, 4];
const [, object, three, four] = obj;
console.log(object); //{a: 1, b:2}
In this example, object returns {a: 1, b:2} but I wanted it change the value instead. Is that possible?
thanks, regards.
You are confusing default values with mutation of values, and assignment of values to variables with mutation of objects. Below is a demo of the default value feature of destructuring, with comments to explain the behavior.
You will see here that in general, destructuring is not designed for mutation of objects, but for extraction of variables and values. And hopefully also get a feel for why it would be undesirable for mutation to be mixed in to it, even if it were possible.
const obj = [1, {a: 1, b:2, 99:'z'}, ,3, 4, {mutateme: 1}];
const [, {a=3,b=4,c=5}, object={a:7,b:7},three, four, object2] = obj;
// a prop has value=1, b has value=2, c is not defined use default value 5
console.log(a,b,c,object);
//object is empty use default value={a:7,b:7}
// obj is unchanged
console.log(obj)
// mutate object2={mutateme:1} by reference (like a pointer)
object2.mutateme=7
// {mutateme: 1=>7}
console.log(obj)
// example of how you could (sort of) mutate inside a destructuring statement
// computed property, obj[1]=obj[3]=99 returns 99,
// so extract property 99 to variable z and mutate object obj at index [1] and [3] to =99
// y will 99 now.
const [y1, {[obj[1]=obj[3]=99]:z},, y2 ] = obj
console.log(y1, z, y2)
// if something similar were built into destructuring syntax,
// can you imagine how confusing it could get, and cause of all kinds of unexpected behavior?