The JavaScript Programming Language

Statement

Statement ends with semicolon.

var x = y >= 0 ? y : -y;

 

 

Expression

Expressions are collections of statements mostly inside blocks.

var x;

if (y >= 0) {
   x = y;
} else {
   x = -y;
}

 

Block

Block is a collection of statements inside curly braces.

if (x<=y) {

   x += 3;

   y = 23;

}

 

Semicolons

Semicolons terminate statements.

var x = 23;

var fja = function ( x ) { ... };   //only case where block ends with semicolon

 

AUTOMATIC SEMICOLON INSERTION

JS parser insert semicolon automatically:

• newline     if (x < 0) x = 0
• inside curly brace     function add(x,y) { return z }

 

Sometimes generate error:

return
{
name: 'John'
};

return ; //automatic insertion generate error
{
name: 'John'
};

 

 

Comments

// single line

 

/*

multi line

comment

*/

 

Variables and assignement

Variables are defined by var keyword.

var identifier = value;

var x = 5;

x = 8; //overwrite variable

console.log(x); //8

 

VARIABLE IDENTIFIER

Identifier is a variable name. It can contain any unicode characters for example čćž.

var čćž = 15;  //croatian characters

console.log(čćž);

 

example: 001syntax_unicode.js

 

"café" === "caf\u00e9"      //true

 

Identifier must start with character, _ or $. Can't start with number.

var 3x ;  //this will generate error

 

Also don't use reserved words for identifier.