Javascript concepts

Values & References

• primitive types: Boolean, null, undefined, String, and Number

• Reference types: Array, Function, and Object.

• functions creates a new variables for each parameter

• equality operators == and ===

Scope vs Context

Scope refers to the visibility of variables

• let and const keeps the scope

Context refers to the value of this in the same scope (window obj in browser and node obj in app)

• new logFunc() // creates a local context appoint to the same function
• if / switch / for /while don’t create contexts so the context will be the same as it’s parent

*JavaScript is a single-threaded language so it can only execute a single task at a time. The rest of the tasks are queued in the Execution Context.

IIFE (Immediately Invokable Function Expressions)

(function(){ alert("Name: " + name); }());

Hoisting

node move the declarations to the top using the browser or node memory space *To avoid hoisting use anonymous function

Closure

A closure is the combination of a function bundled together (enclosed) with references to its surrounding state (the lexical environment). *Functions that returns functions *closure are promises? Promises are a different concept *Understand that closures allow data hiding, memoization, and dynamic function generation.

This

• The JavaScript this keyword refers to the object it belongs to:
• in global object refers to window or node object.
• in a method the class
• in a function, this refers to the global object (if it's not strict mode, otherwise is undefined).
• In an event, this refers to the element that received the event.
• Methods like call(), and apply() can refer to any object.

New (keyword)

It creates the local this point and adds proto functionalities like a constructor for instance.

Call vs apply vs bind

• Call you pass as argument the obj that you want as a context from a method - method.call(myNewContext)
• Apply is the same thing as call but you must send the parameters as a list.
• Bind is the same as call but returns the method instead of call it.

Pure Functions