Javascript

Reference

• JavaScript and HTML DOM reference on w3schools.com
• Web API on mozilla.org
• Mozilla tutorials

Syntax

JS type

// Strings
var carname = "Volvo XC60";

// Numbers
var x = 3.14;
var y = 34;

JS operators

// Arithmetic operators
x = y + 2;
x = y - 2;
x = y * 2;
x = y / 2;
x = y % 2;       // Modulus (division remainder)
x = ++y;         // Pre-increment
x = y++;         // Post-increment
x = --y;         // Pre-decrement
x = y--;         // Post-decrement

// Assignment operators
x = y;
x += y;
x -= y;
x *= y;
x /= y;
x %= y;

// String operators
text3 = text1 + text2;     // Concatenation
text1 += text2;

// Comparison operators
x == 8;    // equal to
x === 5;   // equal value and equal type
x != 8     // not equal
x !== 5    // not equal value or not equal type
x > 5;
x < 5;
x >= 5;
x <= 5;

// Ternary operator
voteable = (age < 18) ? "Too young" : "Old enough";

// Logical operators
x && y;     // logical and
x || y;     // logical or
!x;         // not

// Bitwise operators
x = 5 & 1;  // bitwise and
x = 5 | 1;  // bitwise or
x = ~5;     // bitwise not
x = 5 ^ 1;  // bitwise xor
x = 5 << 1; // bitwise left shift
x = 5 >> 1; // bitwise right shift

// typeof
typeof "John";            // returns string

// delete
var person = {firstName:"John", lastName:"Doe", age:50, eyeColor:"blue"};
delete person.age;        // or delete person["age"] -- delete property from an object

// in
var cars = ["Saab", "Volvo", "BMW"];
"length" in cars          // true if property is in the specified object
"firstname" in person

// instanceof
cars instanceof Array;    // true if object is instance of specified class

// void
void(0);                  // evaluate expressions and returns undefined

JS statements

// switch
switch(fruits) {
    case "Banana":
        text = "Banana is good!";
        break;
    default:
        text = "I have never heard of that fruit...";
}

// while
while (i < 5) {
    // ...
}

JS functions

var myfct = function(arg1, arg2) {
     return arg1 + ", " + arg2;
}
myfct("Hello", "World");

General information

$ aka jQuery

jQuery is a fast, small, and feature-rich JavaScript library for HTML manipulation...

In Javascript, jQuery library is often exported as the dollar symbol, $!

How-to

Wait until a function is loaded

We fire a setTimeout event until the function is available [1]:

$(function(){
    $("#loadingGIF").show();
    WaitForFunction();
});

function WaitForFunction()
{
    // Here we should use (typeof FUNCTION_TO_WAIT_ON_HERE === "function")
    // See https://stackoverflow.com/questions/12206083/whats-the-difference-between-typeof-variable-function-and-jquery-isfunc
    if (!$.isFunction(FUNCTION_TO_WAIT_ON_HERE)) {
       setTimeout( WaitForFunction, 100);
       return;
    }
    Function_Loaded();
}

function Function_Loaded(){
      $("#loadingGIF").hide();
}

Note that the code is not recursive because setTimeout does not call the given function but add it to a timer event queue.

Simulate click on a button

Use jQuery [2]:

$('#mybutton').trigger('click');
$('#mybutton').click();          // Simpler

View object attributes

for (var attr in obj) { console.log ("Attribute " + attr + " is: " + obj[attr]); }

Add property to an undefined object

If we want to add a property to an object that is not yet defined, just assign the value {} to it.

var myobj = {};
myobj.someProperty = "value";

// or...

window.myobj = {};
window.myobj.someProperty = "value";

How to sleep / wait for a delay

Just don't, because it would block the execution thread. Instead, fire a time event with setTimeout [3]:

setTimeout(function(){alert("hi")}, 1000);

Build

Grunt: the Javascript Task Runner

• https://gruntjs.com/getting-started

grunt          // Run default task (usually build), equiv. to "make"

Debug

Firefox

• In Firefox, Ctrl-Shift-C to open up the console and debugger tools.\
• To browse an object, go to the console, and type the name of an object to open it up in the object explorer. For instance, to browse from the global context window:

>> windows