Web Developer| Biochemist|Language Lerner|Music

Web Developer| Biochemist|Language Lerner|Music

What I learned today | Functional Javascript: Variables Scope and Closures

What I learned today | Functional Javascript: Variables Scope and Closures

Remember the Book: Functional JavaScript

 

So chapter 3 right?…hm

Scopes

From my understanding, where a variable lives, while the extent of a scope means how long a variable holds a value.

Global Scope

  • This has the longest lifespan
  • when you declare a variable without the var, you are defining a global variable (accessible to every function and method in the program)

Lexical Scope

  • refers to the visibility of a variable and its value
  • If I understood correctly, the closest variable value takes precedence

Dynamic Scope

  • The value at the top of the stack in a binding is the current value
  • The poison of dynamic scoping (quote): the value of any given binding cannot be known until the caller of any function is known

This reference

  • Can point to different values depending on the context in which it was first created
  • but it is also determined by the caller
  • can be manipulated through the use of apply or call
    • the referenced object, is whatever object is passed into them as the first argument
  • powerful but dangerous
    • with great power comes great.. oooh pizza!
  • using underscore’s _.bind method can lock the this reference from changing

Function Scope

  • each function can refer to a this reference
  • in JS, all var declarations in a function body are implicitly moved to the top of the function in which they occur
    • rearrangement of variable declarations in Javascript is called hoisting
  • Any code in the function can see al the variables defined inside ergh…

Closures

  • a function that captures values near where it was created
  •  when it captures a value, the value’s lifespan can be extended
    • not only local variables but also arguments can be captured as well
  • they can see all the variables declared within the function they live in

Free variables

  • related to closures
  • are easily captured by inner functions

Shadowing

  • occurs in Js when a variable of a name y is declared within a certain scope and then another variable od the same name is declared in a lower scope
  • here the innermost value takes precedence

Basically,

Closures provide protection and private access when used right

See the Pen Functional Javascript: Scope by Ajala Comfort (@AJALACOMFORT) on CodePen.


So that is all for today, if you want detailed explanation of the topic / chapter, do purchase the book. See ya

 



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