My notes on JavaScript

I started study JavaScript about one years ago, I studied the basic rule and then, due to my work, I moved quickly to use some framework (Ionic and Angular) so I omitted to study it in depth and also  the best practise... Because of this bad start, this December, I re-started to study and I'm writing some notes (mainly on different things than other languages).

Variables

• keyword const, to declare a constant.
• Number:
• Number.NEGATIVE_INFINITY<Number.MIN_VALUE<Number.MAX_VALUE<Number.POSITIVE_INFINITY.
• Math is an "object" with the most common mathematic functions.
• Some useful method of Number: parseInt(), parseFloat(), isNaN(), isInfinite().
• Multiline string, useful to include variable values into the string:

      var a=2;
      var b=2;
      var myString=`this is
                    my value ${a+b} `;

The if statement

• To test if an array is empty, simply use if(myArray.length) not if(myArray.length>0).
• To test if a string is void use if(myString).
• Test only if an object is null if(myObj===null) not if it's null and undefined.

The scope

The scope is a "nested chain": the variable definition is searched in the nested scope, if there isn't then it's search in the upper scope.

• more about scope in Stack Overflow
• Immediately Invoked Function Expression on wikipedia
• Loops and if statement don't have their own scope in ES5, but ES6 introduced it (key-word let).

Functions

The functions parameters are stored in an object (arguments), similar to an array, so it's possible to retrive parameters with: arguments[i].

Collections

• Array
• it can stores several type.
• it's a map, the key is the index. The length() method return the last index plus 1, so 

      var a=2;
      var myArray=[];
      myArray[25]="myLastObject";
      console.log(myArray.length()); //print 26
  

• Usefull methods: foreach, concat, join, pop, push, shift, unshift, reverse, sort.
• Maps, only in ES6.
• Sets, only in ES6.

Tools

• bower, package manager.
• npm, pakage manager.
• javascriptlint
• gulp, builder, it's possible run several task (lint, minify resources..).