Symbol.iterator in Ripple codebase.

#ripple #opensource

In this article, we review Symbol.iterator in Ripple codebase. We will look at:

What is Symbol.iterator?
Symbol.iterator in Ripple codebase.

What is Symbol.iterator?

The Symbol.iterator static data property represents the well-known symbol Symbol.iterator. The iterable protocol looks up this symbol for the method that returns the iterator for an object. In order for an object to be iterable, it must have an [Symbol.iterator] key. — Mdn docs

Example

const iterable = {};

iterable[Symbol.iterator] = function* () {
  yield 1;
  yield 2;
  yield 3;
};

console.log([...iterable]);
// Expected output: Array [1, 2, 3]

Whenever an object needs to be iterated (such as at the beginning of a for...of loop), its [Symbol.iterator]() method is called with no arguments, and the returned iterator is used to obtain the values to be iterated.

Some built-in types have a default iteration behavior, while other types (such as Object) do not. Some built-in types with a [Symbol.iterator]() method are:

Symbol.iterator in Ripple codebase

At L4 in packages/ripple/src/runtime/array.js, you will find the following code:

var symbol_iterator = Symbol.iterator;

and this is one of items in the array:

const introspect_methods = [
 'entries',
 'every',
 ...
 'toLocaleString',
 ...
 'toString',
 symbol_iterator,
 'values',
 'with',
];

and this introspect_methods is called in init function as shown below:

#init() {
  var proto = RippleArray.prototype;
  var array_proto = Array.prototype;

  for (const method of introspect_methods) {
   proto[method] = function (...v) {
    this.$length;
    get_all_elements(this);
    return array_proto[method].apply(this, v);
   };
  }
}