Lexical Structure

Character set

Unicode
which is a computing industry standard for the consistent

 encoding, representation and handling of text 

expressed in most of the world's writing systems

JavaScript 

uses UTF16 code units internally

externally, the browser determines the encoding

LEXICAL STRUCTURE

to support older technology 

that can not display or input the full set of Unicode characters,

unicode escapes have been defined 

\u followed by four hexadecimal digits

\u000A 
  // => UNICODE CHARACTER 'LINE FEED (LF)' (U+000A)

\u00E2 
  // => LATIN SMALL LETTER A WITH CIRCUMFLEX (U+00E2)

Lexical Structure

Case sensitivity

capitalization of letters matters

keywords / variables / function names 

& 

all other identifiers must always be typed 

with a consistent capitalization

the for keyword for example

must be always typed with small caps

NOT

For  /  FOR

LEXICAL STRUCTURE

 <button onClick="someFunction()">Click Me</button>

LEXICAL STRUCTURE

Comments

JavaScript supports two styles of comments

block

/*  ...  */ 

&

single-line comments

// ...

LEXICAL STRUCTURE

var str = "JavaScript";
/*var regex = /[A-Z]*/; str.replace(regex, '_');*/ 

Lexical StructureS

Literals

literals are fixed values  NOT variables

that are literally provided in a script

LEXICAL STRUCTURES

Lexical Structure

Numeric Literals

JavaScript has a single number type

10     //=> 10 - number ten1.5    //=> 1.5 - number one point five
.2     //=> 0.2 - number zero point two1e2    //=> 100 - number one hundred-1     //=> -1 - number minus one020    //=> 16 - number sixteen in base 8 (octal)
0x10   //=> 16 - number sixteen in base 16 (hexadecimal (hex))
[0xff, 0x00, 0x00] //=>  [255, 0, 0] - it looks like?

LEXICAL STRUCTURE

parseInt('JavaScript');   //=> NaN

typeof NaN  //=> "number"

NaN === NaN   //=> false

LEXICAL STRUCTURE

Infinity

represents all values greater than

1.79769313486231570e+308

or

1.79769313486231570 × 10³⁰⁸

1.79769313486231570e+309       //=> Infinity

Lexical Structure

String Literals

'JavaScript'   //=> "JavaScript"
"JavaScript"   //=> "JavaScript"
''             //=> ""
""             //=> ""
"\u005C"       //=> "\"

LEXICAL STRUCTURE

Boolean Literals

represented by two literal values

true & false

Lexical Structure

Object Literals

represented by a list of zero or more pairs of 

property names & associated values 

enclosed in curly brackets

var course = {   name: 'Javasript - The Basics'};
console.log(course); //=> Object {name: "Javasript - The Basics"}

LEXICAL STRUCTURE

Array Literals

var course = ['JavaSript', 'The Basics'];
console.log(course); //=> ["JavaSript", "The Basics"]

Lexical Structure

A function literal defines a function value
formed by

function keyword / optional name

list of parameters  / function body

var name = function (param1, param2, param3) {
  (function () {   console.log(param1, param2, param3);  })();
}
name('JavaScript', '-', 'The Basics');    //=> JavaScript - The Basics

LEXICAL STRUCTURE

Regular Expression Literals

provide compilation of the
regular expression when the script is loaded

var regex = /[A-Za-z0-9]/g;

Lexical Structure

Identifiers

used to

name variables & functions

or 

to provide

labels for certain loops

LEXICAL STRUCTURE 

identifiers must begin with 

a letter 

an underscore _

followed by

letters / digits / underscores / dollar signs

digits are not allowed as the first character

use only ASCII letters

LEXICAL STRUCTURE

Reserved Words

are keywords

reserved by the language

&

cannot be used as identifiers

LEXICAL STRUCTURE

LEXICAL STRUCTURE

avoid using predefined global variables

&

function names

arguments / Array / Boolean / Date 

decodeURI / decodeURIComponent / encodeURI / encodeURIComponent 

Error / eval / EvalError / Function / Infinity / isFinite / isNaN / JSON

NaN / Number / Object /  parseFloat / parseInt / RangeError / ReferenceError

RegExp / String / SyntaxError / TypeError / undefined / Math

have in mind that JavaScript implementations 

may define other global variables & functions

LEXICAL STRUCTURE

Optional Semicolons

the semicolon ; is used to separate statements 

to make the code clearer

it CAN usually be omitted

between two statements 

if those statements are written on separate lines

at the end of a program

before a closing curly bracket }

Lexical Structure

JavaScript treats a line break as a semicolon if the 

next non space character cannot be interpreted as a continuation

of the current statement 

var last = 'JavaScript'var first = 'The Basics'var name = last + first

(last + first).toUpperCase()     //=> TypeError: string is not a function

LEXICAL STRUCTURE

return
true;
// is interpreted as:
return; true;// even if you meant:return true; 

LEXICAL STRUCTURE

i
++
j

// is parsed as:
i; ++j;
// not as:
i++; j;