//How to make a comment on the code? //How to declare a variable? /** * (Multiline comment) * Variable's name can start with letter, uncerscore(_). * You can use numbers, but not in the first character of the variable's name.. * */ let x = 1000; // Visible only inside the block scope (Between curly braces - "{}") var y = 2000.65; // Visible on the application scope (hoisting - elevated context) //How to show the variables on console? console.log(x + y); //How to print something on the document. Use it just for test output. document.writeln(x); // or without break line: document.write(x); //How to alocate Strings on variable? /** * You can do double quotes inside of double quotes * using the escape character: \" or \' (inside of single quotes). * */ var strDoubleQuotes = "Hi! i'm a string and i'm between double quotes!"; var strSingleQuotes = 'Hi! i\'m a string and i\'m between single quotes!'; document.writeln("
String output 1 => " + strDoubleQuotes); document.writeln("
String output 2 => " + strSingleQuotes); //How to declare boolean variable? var bool1 = true; var bool2 = false; document.writeln("
Boolean 1 = " + bool1); document.writeln("
Boolean 2 = " + bool2); //How to use operators in JS? var a = 30; var b = 20; var sum = a + b; var mult = a * b; var incr = a++; var decr = a--; var div = a / b; //How to evaluate a String expression? var expr1 = eval("a + b"); document.write("
String expression reult: " + expr1); var expr2 = eval("a / b"); document.write("
String expression reult: " + expr2); var expr3 = '4' / '5'; document.write("
String expression reult: " + expr3); var expr4 = 'someLetter' * '9'; // Results NaN document.write("
String expression reult: " + expr4); //How to handle division by 0 (zero)? try { document.writeln("
Trying to divide " + a + "by 0: " + a / 0); throw new Exception(); } catch (exception){ document.writeln("
Division by 0 causes an exception"); } //How to get division remainder? document.writeln("
Modulus Operand: " + a + " % " + b + " = " + a % b); //How to use assignment operators? document.writeln("
Assignment operators - After " + a + " += " + b + " we have " + (a + b)); document.writeln("
Assignment operators - After " + a + " *= " + b + " we have " + (a * b)); document.writeln("
Assignment operators - After " + a + " /= " + b + " we have " + (a / b)); document.writeln("
Assignment operators - After " + a + " -= " + b + " we have " + (a - b)); document.writeln("
Assignment operators - After " + a + " %= " + b + " we have " + (a % b)); //Comparison operators document.writeln("
Comparison operator: a = " + a + ". So a == 8 = " + (a == 8)); //Data types var data; document.writeln("
" + typeof data) var data = 1; document.writeln("
" + typeof data) var data = "1"; document.writeln("
" + typeof data) var data = {}; document.writeln("
" + typeof data) var data = function dataFunc() {} document.writeln("
" + typeof data) //To be continued...

JS Guide