Javascript

Javascript is case sensitive

/* Block Comment
 */
var a = "Hello World!"; // Line Comment
document.write(a+"<br>");

var x = 1, y = 2;
document.write(x+y)

var a = 10, b = 100;

document.write("a + b = " + (a+b) + "<br>"); // +
document.write("a - b = " + (a-b) + "<br>"); // -
document.write("a * b = " + (a*b) + "<br>"); // *
document.write("a / b = " + (a/b) + "<br>"); // /
document.write("a ** 2 = " + (a**2) + "<br>"); // **, exponentiation
document.write("a % 3 = " + (a%b) + "<br>"); // / %, modulus
document.write("++a = " + (++a) + "<br>"); // ++
document.write("--a = " + (--a) + "<br>"); // --

a += 1;
a -= 1;
a *= 2;
a /= 2;

// primitive type, immutable
var a = 10;
var b = a; // create a copy of a, a and b point to the same object

console.log("a: "+a+" b: "+b+"<br>"); // a: 10 b: 10

b = 100; // create a new object, let b point to the created object
console.log("a: "+a+" b: "+b+"<br>"); // a: 10 b: 100

// object, mutable
var car = {color: 'blue', maker: 'Honda'};
var car2 = car; // car and car2 point to the same object

console.log(car); // {color: "blue", maker: "Honda"}
console.log(car2); // {color: "blue", maker: "Honda"}

car2.color = 'red';

console.log(car); // {color: "red", maker: "Honda"}
console.log(car2); // {color: "red", maker: "Honda"}

A variable can be used before it has been declared

x = 10;

console.log(x);

var x;

With strict mode, can not use undeclared variables

Strict mode is declared by adding "use strict"; to the beginning of a script or a function

Declared at the beginning of a script, it has global scope

"use strict";
x = 3.14;

"use strict";
var obj = {};
Object.defineProperty(obj, "x", {value:0, writable:false});

console.log(obj);

//obj.x = 3.14;   // This will cause an error