JavaScript

1. Define and initialize variable

    var myVariable;
    myVariable = "my string";

    var myVariable = "my string";

2. Define and call function

    var myFunction = function(myArgument) {
    };
   
    myFunction("my argument");

    function myFunction(myArgument) {
    };
   
    myFunction();

3. Comments

    //single line comment

   /*
   multi 
   line 
   comment
   */

4. Write to console

    console.log();

5. Get symbol from string

    var myString = "my string";
    var symbol = myString[1];

6. Get substring from string

    var myString = "my string";
    var symbol = myString.slice(1, 5); //including, excluding

7. Change case of string

    var myString = "my string";
    var myStringUpper = myString.toUpperCase();
    var myStringLower = mySrting.toLowerCase();

8. Equals

    == //aproximate equals
    === //sharp equals

   1. Empty variable

      undefined //means no value by default
      null //manually set no value

9. Array

    var myArray = [ 1, 2, 3, "4", "5", true, false, 1.5 ];
   
    console.log(myArray[3]);
   
    myArray[3] = 33;
   
    console.log(myArray.length);
   
    myArray.push("Cat"); //add element to the end of array, returns length of array
   
    myArray.unshift("Dog"); //add element to the beginning of array, returns length of array
   
    myArray.pop(); //delete last element of array, returns deleted element
   
    myArray.shift(); //delete first element of array, returns deleted element
   
    myArray concat array1, array2
   
    myArray.join(); //transform array to string
    myArray.join("*"); //transform array to string with custom separator
   

10. Random

     Math.floor(Math.random() * 5); //random from 0 (including) till 5 (not including)
    

11. Objects

     var cat = {
         "legs" : 4,
         "name" : "Snow"
     }
    
     var cat = {
         legs : 4,
         name : "Snow"
     }
    
     cat["name"];
     cat[name];
    
     Object.keys(cat);
    
     var object = {};
    
    object[name] = "Snow";
    object.legs = 4;
    
    console.log(object.name);

12. conditions and loops

     if (true) {
         //do something
     } else if (false) {
         //do something
     } else {
         //do something
     }
    
     while (true) {
         //do something
     }
    
     for (var i = 0; i < 10; i++) {
         //do something
     }

13. popups

     alert("Warning");
    
     if (confirm("Confirm")) {
         //d osomething
     }
    
     var result = prompt("some prompt text", "default value");