Let’s review some JavaScript features in a hurry!
Iterables
Objects that can be used in for..of are called iterable.
Iterables must implement the method named Symbol.iterator. The result
of obj[Symbol.iterator] is called an iterator. An iterator must have
the method named next() that returns an object {done: Boolean, value:
any}, the value is the next value. The Symbol.iterator method is
called automatically by for..of, but we also can do it directly.
Array.from(obj[, mapFn, thisArg]) makes a real Array of an iterable or
array-like obj, and we can then use array methods on it. The optional
arguments mapFn and thisArg allow us to apply a function to each item.
Destructuring
Map an object or array to variables.
Object syntax:
let {prop : varName = default, ...} = object
Array syntax:
let [item1 = default, item2, ...rest] = array
The first item goes to item1; the second goes into item2, all the rest
makes the array rest.
Map and Set
Map, is a collection of keyed values, it allows objects to be keys and
provides a size property.
Set, is a collection of unique values, does not allow to reorder elements.
The following allow garbage-collection:
There ara also WeakMap and WeakSet which provide garbage collection,
I need to research more about these. Maybe the next post.
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