Monday, November 20, 2017

RxJS: Reactive Extensions for Javascript

What is reactive extensions?

It's the Javascript version of a library that has been commonly used for a few years in many other languages including C#. It's main construct is the Observable and the operators that can be applied to it.


Because Reactive Extensions is now common practice in Angular and React development, and in combination with a store, is now adding and altering the MVC that has been also very popular in web development in the last decade or so.

In the next few posts, I will be writing about RxJS constructs, whit a focus on summarizing some common observable operators.

ES6: Generators

Generator functions definitions are prefixed with an asterisk and the function body contains one or more yield statement.

Each time the generator is invoked, it will continue until the next yield statement, where it can return with or without a return value.

Friday, November 17, 2017

ES6: tag functions

tag functions act as pre processors for a template literal.
They receive a strings param, and each value is an paramter, which is usually gathered using the rest operator.
They have been used for various implementation, including the JSX parser used by React to parse html.

ES6: object literal property shorthands

New shorthands for properties having the same name as the variable assigned to them, concise properties.

Shorthand for functions, concise functions, although the underlying function is anonymous therefore cannot be reference, for example in the case of recursion.

Also computed property names allows the use of variables as property names, inside object literals, using square brackets.

And template literals were added, the backtick operator used designate an interpolatable string where variables are surrounded by curly braces and preceded by a dollar sign.

ES6: Destructuring

Destructuring can be used to extract data with arrays or objects, in a declarative way, and is self documenting, allowing the next developer to read, to understand a lot about the intent of this line of code.

It is particularly useful to extract data from an array, because the destructing pattern reveals the shape of the data, and the name of the variables used in the pattern show what is the important data we want to extract from this array, or multidimensional array.

Note that it is possible to chain multiple destructring patterns, since each of them returns the original array.

When destructuring objects, the destructuring pattern uses curly braces, with the source property name on the left, and target variable on the right.
In the case the two are the same, in ES6, they don't need to be repeated.
It is also possible to destructure nested objects, in this case a nested destructuring pattern would be provided.

ES6: Spread vs Gather operators

These new operators, both represented by dot dot dot, has two purpose, to gather arguments, or spread them.

One quick note about the gather operator, it is sometimes referred to as the 'rest' operator, not the verb resting, but rest as a noun.

In the context of a function declaration, a ... before a variable with gather all the arguments in one variable.

In the context of a function invocation, a ... operator would spread them out, as arguments passed in.

Thursday, November 16, 2017

ES6 const, vs Object.freeze

The purpose of const is to prevent reassignment of a variable.
But it won't make it immutable, this can be done using Object.freeze.