JavaScript Syntax Refresher

by horhey

JavaScript

// This is an example of a single-line comment.
 
/*
 * this is an example
 * of a
 * multi-line
 * comment.
 */

// Whitespace is insignificant.
var hello = "Hello";
var world     =      "World!";

// Readable code is good!
var foo = function() {
 
    for ( var i = 0; i < 10; i++ ) {
 
        alert( i );
 
    }
 
};
 
foo();
 
// This is much harder to read!
var foo=function() {for(var i=0;i<10;i++){alert(i);}};foo();

/* reserved words:
break, case, catch, class, const, continue, debugger, default, delete, do, else, enum, export, extends, false, finally, for, function, if, implements, import, in, instanceof, interface, let, new, null, package, private, protected, public, return, static, super, switch, this, throw, true, try, typeof, var, void, while, with, yield
*/

// Valid identifier names.
var myAwesomeVariable = "a";
var myAwesomeVariable2 = "b";
var my_awesome_variable = "c";
var $my_AwesomeVariable = "d";
var _my_awesome_variable_$ = "e";

// This works:
var test = 1;
var test2 = function() { ... };
var test3 = test2( test );
 
// And so does this:
var test4 = 1,
    test5 = function() { ... },
    test6 = test2( test );

// declared but non-defined vars are "undefined"
var x;
console.log(x === undefined); // true

// Concatenation
var foo = "hello";
var bar = "world";
 
console.log( foo + " " + bar ); // "hello world"

// Multiplication and division
console.log(2 * 3);
console.log(2 / 3);

// Incrementing and decrementing
// The pre-increment operator increments the operand before any further processing.
var i = 1;
console.log( ++i ); // 2 - because i was incremented before evaluation
console.log( i );   // 2
 
// The post-increment operator increments the operand after processing it.
var i = 1;
console.log( i++ ); // 1 - because i was evaluated to 1 and _then_ incremented
console.log( i );   // 2 - incremented after using it

// Addition vs. Concatenation
var foo = 1;
var bar = "2";
 
console.log( foo + bar ); // 12

// Logical AND and OR operators
...