Javascript Basics Part I

I was going through many of the Douglas Crockford videos on Javascript and came across many of the oddities in the Javascript language. I was highly impressed by his outspoken admission on some of the features of the languages being “bad”. But at the same time, he highlighted that Javascript is one of the most widely mis-understood programming languages and there are many powerful features which are quite powerful.

Value Types (Everything else is objects)

  • Number
  • Strings
  • Booleans
  • Objects
  • null
  • undefined

Few points about NaN:

  • NaN stands for Not a number
  • NaN does not equal to anything, including Nan
  • Nan is a number type.
  • type of Nan is Number

Number function

Number(value)

  • Convert a string to a number

parseInt function

parseInt(value, 10)

  • The radix (10) should be required

Math object

  • Math object is modeled on Java’s Math class

Strings

  • Strings are immutable
  • Similar strings are equal (==). Jave got that wrong
  • Strings literals can use single or double quotes
  • string.length determines the length of string

String function

string(value)

  • Convert a number to String

Boolean function

Boolean(value)

  • returns true if the value is truthy
  • returns false if the value is falsy
  • Similar to !! operator

Falsy Values

  • false
  • null
  • undefined
  • ””
  • 0
  • Nan

Truthy Values

  • All other values (including all objects) are truthy including "0" , "false"

  • undefined is the default value for variables
  • Thus, a variable can be defined and also undefined at the same time :)

Dynamic objects

  • new Object() produces an empty container of name/value pairs
  • A name can be any string, a value can be any value except undefined
  • members can be accessed with dot notation or subscript notation

Loosely typed

  • Any variable can recieve or send any type of parameter
  • Language is not untyped

Reserved words

  • Many of hte words are reserved but only handful of them are being used in language

== and != operators

  • These operators can do type coercion
  • It is better to use === and !==, which do not do type coercion.

&& Guard operator (Logical AND)###

  • If first operand is truthy then result is second operand else result is first operand
  • It can be used to avoid null references
if (a)
{
	return a.member;
}
else
{
	return a;
}
  • It can be written as return a && a.member;

|| Default operator (Logical OR)###

  • If first operand is truthy then result is first operand else result is second operand
  • It can be used to fill in default values. var last = input || nr_items;