How does dot notion work in array or different places

Question

I have been trying to understand dot notion and how can we create dot notion

Simply state, consider this example

const a = [1,2,3,4,5,7].reduce((a, i) => a*i)

Here how can we use dot notion.

From my understanding, we use dot notion in case of object.

probably Array have a prototype named reduce? and reduce accepts 4 arguments.

But how do we tell reduce to iterate over the loop. We aren't passing it the entire array?

@NinaScholz `.` `.map` or `.reduce` (just the dot). like using `.lowerCase()`, `.toString` — Diza Moa, Dec 05 '20 at 14:09
you are using it as [property accessor](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Property_Accessors). — Nina Scholz, Dec 05 '20 at 14:10
@NinaScholz right. then in case of **Arrays** , when we used `.map` or `.forEach` or in case of `string`, when we use `.toLowerCase()`, how does it knows that we need to iterate (in case of array)? like we aren't passing array to function arguments? — Diza Moa, Dec 05 '20 at 14:12

score 1 · Answer 1 · answered Dec 05 '20 at 14:33

1

When we add any method to prototype of the class we can always access the instance of the class on which this method is called by this.

Array.prototype.test = function(){
  console.log(this);
};
[1,2,3].test()

answered Dec 05 '20 at 14:33

Maheer Ali

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score 0 · Answer 2 · answered Dec 05 '20 at 14:38

The reduce function is a built in javascript function which works only with arrays.

You don't tell explicitly to 'reduce' to iterate all over the array because it(reduce function) is already coded such that it does something(add, sum, multiply, whatever expression you may provide) with that array.

If you really want to know what is going on the background, you can see this torque file which is from V8 engine's source code==>https://github.com/v8/v8/blob/master/src/builtins/array-reduce.tq

From what I understood, it also uses a for loop inside the function.

For that you should also have understanding of TorqueScript.

You can check any open source engine for that matter.For more details about how to view the code and where exactly, visit this link==>https://stackoverflow.com/questions/22300206/how-to-see-the-source-of-built-in-javascript-functions

So to answer your question => it simply just calls reduce and rest of the work is taken care by it in the background, that's not really associated with 'dot notion'.

FZs · Answer 3 · 2020-12-05T14:54:57.547

Arrays are special objects. But the usability of dot notation doesn't depend on the object, but rather the property you want to access.

Also note that foo.bar is the same as foo['bar'].

You can always use bracket notation. On the other hand, dot notation can only be used if the property is a valid identifier (consists of letters, numbers, $s and _s, and can't begin with a number).

That shows the reason why we can't access arrays' indices with it, as they are numbers (so they also begin with numbers).

The bracket notation is also required if you want to access a key named the result of evaluating an expression.

So:

const object = {
  0: 1,
  foo: 2,
  'key with spaces': 3,
  '3D': 4,
  'D3': 5
}
const array = [1, 2, 3]

//These are okay...
object.foo
object['foo']
array.reduce
array['reduce']
object[0]
array[0]
object['0']
array['0']
object['key with spaces']
object['3D']
object.D3
object['D3']
object['f' + 'o'.repeat(2)]
array[array.length-2]

//...but these are not:

object.0
array.0
object.key with spaces
object.3D //begins with a number

How does dot notion work in array or different places

3 Answers3