Javascript

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Javascript

Subpage Table of Contents

Load Script

External Script 

<script type="text/javascript" src="myscript.js"></script>

Inline: (in html head or body) 

<script type="text/JavaScript">
<!--
  // some javascript...
//   -->
</script>

References

DevGuru JavaScript Quick Reference Methods Index

Page Refresh

Example: [1] 

<a href="javascript:location.reload(true)">Refresh this page</a>

Other triggers: 

<input type="button" value="Reload Page" onClick="window.location.reload()">
<input type="button" value="Reload Page" onClick="history.go(0)">
<input type="button" value="Reload Page" onClick="window.location.href=window.location.href">

Auto Page Refresh

Example: [2] 

<!-- Codes by Quackit.com -->
<html>
<head>
<script type="text/JavaScript">
<!--
function timedRefresh(timeoutPeriod) {
	setTimeout("location.reload(true);",timeoutPeriod);
}
//   -->
</script>
</head>
<body onload="JavaScript:timedRefresh(5000);">
<p>This page will refresh every 5 seconds. This is because we're using the 'onload' event to call our function. We are passing in the value '5000', which equals 5 seconds.</p>
<p>But hey, try not to annoy your users too much with unnecessary page refreshes every few seconds!</p>
</body>
</html>

Refresh using META-Refresh

See HTML#META-Refresh

Change span content

Change span content [3] 

document.getElementById("someelement").innerHTML="...";

// 
<span id="posting:oTxtIgnoreAdd" onclick="ChangeText(this)'">Add</span>

...

function ChangeText(field){
  field.innerHTML='Ignore';
}

auto refresh image

<script type="text/javascript" src="camera.js"></script>
<body onload="updateImage();">

...

var newImage = new Image();
newImage.src = "http://localhost/image.jpg";

function updateImage()
{
if(newImage.complete) {
    document.getElementById("theText").src = newImage.src;
    newImage = new Image();
    number++;
    newImage.src = "http://localhost/image/id/image.jpg?time=" + new Date();
}

    setTimeout(updateImage, 1000);
}

Maybe: 

newImage.src = "..." + new Date().getTime();

References:

onclick

<a href="" onhover="dosomething();" onmouseover="dosomethingelse();" onclick="return false;">Do Something</a>

AJAX

function get_active() {
	var xmlhttp;
	if (window.XMLHttpRequest) {// code for IE7+, Firefox, Chrome, Opera, Safari
		xmlhttp=new XMLHttpRequest();
	} else {// code for IE6, IE5
		xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
	}
	xmlhttp.onreadystatechange=function() {
		document.getElementById("status").innerHTML = "Loading...";
		if (xmlhttp.readyState==4 && xmlhttp.status==200) {
			document.getElementById("activesprinkler").value = xmlhttp.responseText;
		}
	}
	xmlhttp.open("GET", "sprinkler.py", true);
	xmlhttp.send();
}

WARNING: don't try opening a file on another server, it won't work, due to security constraints!

AJAX Send an XMLHttpRequest To a Server - http://www.w3schools.com/ajax/ajax_xmlhttprequest_send.asp

AJAX Tutorial - http://www.w3schools.com/ajax/

Detect IE Version

if(navigator.appName.indexOf("Internet Explorer")!=-1){     //yeah, he's using IE
    var badBrowser=(
        navigator.appVersion.indexOf("MSIE 9")==-1 &&   //v9 is ok
        navigator.appVersion.indexOf("MSIE 1")==-1  //v10, 11, 12, etc. is fine
too
    );

    if(badBrowser){
        // navigate to error page
        alert('WARNING: PAGE WILL LOOK BROKEN!\nYou really should upgrade to IE 10, or even better switch to Firefox/Chrome!');
    }
}

Modified from source: http://stackoverflow.com/questions/10964966/detect-ie-version-in-javascript

-- 

function isIE () {
  var myNav = navigator.userAgent.toLowerCase();
  return (myNav.indexOf('msie') != -1) ? parseInt(myNav.split('msie')[1]) : false;
}

if (isIE () < 10) { ... }

Javascript from Command Line

Use the '/usr/bin/js' command.

js - JavaScript interpreter - http://www.mozilla.org/js/

"JavaScript is the Netscape-developed object scripting language used in millions of web pages and server applications worldwide. Netscape's JavaScript is a superset of the ECMA-262 Edition 3 (ECMAScript) standard scripting language, with only mild differences from the published standard."

Based on SpiderMonkey - Information specific to JavaScript in C engine (aka SpiderMonkey) embedding.

WARNING: "Note: Because the JavaScript shell is used as a test environment for the JavaScript engine, the available options and built-in functions can change over time." [4]

WARNING: DOES NOT INCLUDE MANY COMMON JAVASCRIPT OBJECTS AND FUNCTIONS:

  • alert()
  • console.log()
  • Object.getOwnPropertyNames(obj)

Documentation:

Installation: 

# epel or rpmforge
yum install js

Code: 

js> print('hi')
hi

js> 6*7
42

js> function f() {
  return a;
}

js> var a = 34;

js> f()
34

js> Math.random()
0.7849307000430139

js> typeof Math
object

js> var o = new Object();

js> quit()

Script: 

$ js echo.js test1 test2
test1
test2
$ cat echo.js
for (i in arguments) {
  print(arguments[i])
}

Other commands: 

js> help()
JavaScript-C 1.7.0 2007-10-03
Command        Usage                  Description
=======        =====                  ===========
version        version([number])      Get or set JavaScript version number
options        options([option ...])  Get or toggle JavaScript options
load           load(['foo.js' ...])   Load files named by string arguments
readline       readline()             Read a single line from stdin
print          print([exp ...])       Evaluate and print expressions
help           help([name ...])       Display usage and help messages
quit           quit()                 Quit the shell
gc             gc()                   Run the garbage collector
trap           trap([fun, [pc,]] exp) Trap bytecode execution
untrap         untrap(fun[, pc])      Remove a trap
line2pc        line2pc([fun,] line)   Map line number to PC
pc2line        pc2line(fun[, pc])     Map PC to line number
stringsAreUtf8 stringsAreUTF8()       Check if strings are UTF-8 encoded
testUtf8       testUTF8(mode)         Perform UTF-8 tests (modes are 1 to 4)
throwError     throwError()           Throw an error from JS_ReportError
build          build()                Show build date and time
clear          clear([obj])           Clear properties of object
intern         intern(str)            Internalize str in the atom table
clone          clone(fun[, scope])    Clone function object
seal           seal(obj[, deep])      Seal object, or object graph if deep
getpda         getpda(obj)            Get the property descriptors for obj
getslx         getslx(obj)            Get script line extent
toint32        toint32(n)             Testing hook for JS_ValueToInt32
evalcx         evalcx(s[, o])         Evaluate s in optional sandbox object o
    if (s == '' && !o) return new o with eager standard classes
    if (s == 'lazy' && !o) return new o with lazy standard classes

Note: Seems pretty useless, or just a toy. Couldn't figure out how to read/write files, execute programs or do other system level operations (although some version do).

References:

jQuery

See jQuery

Chrome JavaScript Console

You can enter JavaScript manually into Chrome's JavaScript Console. It also has code completion functionality, which is really useful! 

CTRL + SHIFT + J

Best if you start with a blank page: 

about:blank

Enter multi line with 

SHIFT + ENTER

Execute code with 

ENTER

var testf = function(count) {
  for (var i = 0 ; i < count; i++) {
    console.log(i + " x");
  }
};
testf(10);

code

comments

c style comments 

// in line comment
/* multi
   line comment */

variables

var myvar;
var mystr = "hello world\n";
var myint = 1;
var myarray = [];
var mydict = {};
var mybool = false;

alert

Post message alert to browser 

alert("some message");

prompt

Prompt for a response: 

var name = prompt("name");    // null if cancel or x

confirm

var answer = confirm("yes or no?");    // true, false if cancel or x

console

Post message to browser's development console log 

console.log("some message");

math

1 + 1;  //  + - * / %
3 / 2;  // 1.5
3 % 2;  // 1
2 + (3 * 2);  // 8

a > b; // > >= < <=

++i;  i++;  // return value before or after decrement
--i;  i++;  // only makes a difference with inline math (5 + ++i), which you should avoid anyway

x += 1; x -= 1;
x *= 1; x /= 1;

var div = Math.floor(y/x);
var rem = y % x;

fake integer division: [5] 

var num = ~~(a / b);
var num = (a / b) >> 0;

Random: 

Math.random();    // 0.898123...
Math.floor(Math.random() * 4);    // 0, 1, 2, 3

comparision

a == b;   // equal-ish (eg. "5" == 5 or 0 == false)
a === b;  // exactly equal (eg. 5 === 5)
a !== b;  // not exactly equal (eg. 5 !== 4)

boolean

true && false;  // false
true || false;  // true
! true;         // false

strings

"hello";
'hello';
"hello" + "world";
"hello world".slice(2, 4);  // "ll" (start, end+1)
"hello".length;  // 5
"hello"[0];      // "h"
"hello".toUpperCase();
"hello".toLowerCase();

const fruit = ['apple', 'bananna'];
if(fruit.includes('apple', 0)) { ... }

null and undefined

var myVariable;  // myVariable is undefniend (eg. myVariable === undefined)
var myVariable = null;  // myVariable is null - used to deliberately say it is empty (eg. myVariable === null)

if

if (condition) { ... }
else if (condition) { ... }
else { ... }

loops

while (condition) { ... }

// for (setup; condition; increment) { ... }
for (var i = 0; i < max; i++) { ... }

for (var key in obj) { ... }

break;
continue;

function

// function declaration version
function myfunc(var1, var2) { return false; }

// function expression version
var myfunc = function(var) { ... };

// call function
var value = myfunc(var);

--- unlimited arguments --- 

function manyArgs() {
  var args = [];
  for (var i = 0; i < arguments.length; ++i) args[i] = arguments[i];
  // ...
}

function foo() {
  var args = Array.prototype.slice.call(arguments, 0);
  // ...
}

Source: http://stackoverflow.com/questions/6396046/unlimited-arguments-in-a-javascript-function

array

var myarray = [];  // empty array

var myarray = ["1", 2, 3.141];
myarray[0];    // "1"
myarray.length;    // 3
myarray.indexOf("1");    // 0
myarray[myarray.length - 1];    // returns last item (eg 3.141)

myarray.unshift("first");    // returns new size of array and puts item at front
myarray.push("last");    // returns new size of array and puts item on end
myarray.pop();    // returns last item and removes it
myarray.shift();    // returns first item and removes it
// Stacks: Last In, First Out (LIFO)
// Queues: First In, First Out (FIFO)

firstArray.concat(secondArray);    // join 2 arrays
firstArray.concat(secondArray, thirdArray, ...);    // join multiple arrays

var multiarray = ["1", ["name", "date"], 2];
multiarray[1][0];    // "name"

var mystr = myarray.join();    // join array to string separated by commas (no spaces)
var mystr = myarray.join(", ");    // join array to string separated by commas and spaces

var keys = []
for (var key in obj) {
  if (obj.hasOwnProperty(key)) {
    keys.push(key);
}
keys.sort();

random

function getRandomNumber(minimum, maximum) {
  rno = Math.floor(Math.random() * (maximum - minimum + 1)) + minimum;
  return rno
}

json

JSON is native JavaScript Object Notation! 

var testdata = [
                { "apple": { "size": 1163, "color": "red" } },
                { "pumpkin": { "size": 916, "color": "orange" } },
];

Objects

var myemptyobj = {};

// build object with "object literal"
var myobj = {"name": "test",
             "color": "blue"};    // created with an "object literal" - coding whole value all at once
var myobj = {color: "blue",
             "full name": "mr smith"};    // keys are always strings, so quotes only needed with spaces

// access object items
myobj["name"];
var val = myobj[key];
myobj.name;    // dot notation, only works if key doesn't have spaces
Object.keys(myobj);  // array of keys

// build object afterwards
var myobj = {};
myobj["name"] = "mr smith";  // building object afterwards
myobj.color = "blue";  // dot notaiton, only works if key doesn' thave spaces

// array of objects
myarray = [ { name: "test" }, ... ];
myarray[0]["name"];
myarray[0].name;

// functions can be attached, and this object can be referenced with 'this'
myobj.myfunc = function() { ...; this.some_property; }

Classes

There are no classes in JavaScript (no inheritance). Just functions/objects with sub functions/objects/properties.

Advanced Code

Objects Advanced

Constructor - function that creates objects and gives them a set of built-in properties and methods 

var MyObj = function(x, y) { this.x = x; this.y = y; };
var obj = new MyObj(var1, var2);

Prototypes - defines methods for constructor 

var MyObj = function(x, y) { this.x = x; this.y = y; };
MyObj.prototype.draw = function () { ... }
var obj = new MyObj(1, 2);
obj.draw();

Introspection and Reflection

reflection provides a mechanism to self-inspect and manipulate its member attributes and methods 

typeof "John"                // Returns string
typeof 3.14                  // Returns number
typeof false                 // Returns boolean
typeof [1,2,3,4]             // Returns object
typeof {name:'John', age:34} // Returns object 

Object.getOwnPropertyNames(obj);  // Returns all property names

for (var key in obj) { console.log(key); }

Getting an Object's Public Attributes: 

  var getProperties = function(obj) {
    var properties = [];
    for (var prop in obj) {
      if (typeof obj[prop] != 'function') {
        properties.push(prop);
      }
    }
    return properties;
  };

Getting All the Public Methods of a Class 

  var getMethods = function(obj) {
    var methods = [];
    for (var method in obj) {
      if (typeof obj[method] == 'function') {
        methods.push(method);
      }
    }
    return methods;
  };

References:

DOM

Document Object Model (DOM) - access content of a web page 

<h1 id="main">Hello</h1>

var mainElement = document.getElementById("main");
mainElement.innerHTML;
mainElement.innerHTML = newHTML;

Document: 

document.write(someHTML);

Timeout

var timeout_id = setTimeout(func, timeout);  // timeout in milliseconds

clearTimeout(timeout_id);

// Repeating timeout
var timeout_id = setInterval(func, interval);  // interval in milliseconds

jQuery

See jQuery

Canvas

drawing on the canvas 

<canvas id="canvas" width="200" height="200"></canvas>

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

// draw text
ctx.font = "20px Courier";
ctx.fillStyle = "Black";
ctx.textAlign = "left";  // left, center, right
ctx.textBaseline = "top";  // bottom, middle, top
ctx.fillText("hello world", 50, 50);

// draw solid square
ctx.fillStyle = "Red";
ctx.fillRect(0, 0, 10, 10);

// draw rectangle
ctx.strokeStyle = "DeepPink";
ctx.lineWidth = 4;
ctx.strokeRect(10, 10, 100, 20);

// draw lines
ctx.strokeStyle = "Turquoise";
ctx.lineWidth = 4;
ctx.beginPath();
ctx.moveTo(10, 10);
ctx.lineTo(60, 60);
ctx.moveTo(60, 10);
ctx.lineTo(10, 60);
ctx.stroke();

// draw fill path
ctx.fillStyle = "SkyBlue";
ctx.beginPath();
ctx.moveTo(100, 100);
ctx.lineTo(100, 60);
ctx.lineTo(130, 30);
ctx.lineTo(160, 60);
ctx.lineTo(160, 100);
ctx.lineTo(100, 100);
ctx.fill();

// draw circle
// 0 radians = 0 degrees
// pi / 2 radians = 90 degrees
// pi radians = 180 degrees
// pi * 3/2 radians = 270 degrees
// pi * 2 radians = 360 degrees
ctx.lineWidth = 2;
ctx.strokeStyle = "Green";
ctx.beginPath();
ctx.arc(50, 50, 20, 0, Math.PI / 2, false);
ctx.stroke();

// draw circle function
var circle = function (x, y, radius) {
  ctx.beginPath();
  ctx.arc(x, y, radius, 0, Math.PI * 2, false);
  ctx.stroke();
};

Colors: http://css-tricks.com/snippets/css/named-colors-and-hex-equivalents/


--- Sample Bee --- 

<canvas id="canvas" width="200" height="200"></canvas>
<script>
var circle = function (x, y, radius, fillCircle) {
 ctx.beginPath();
 ctx.arc(x, y, radius, 0, Math.PI * 2, false);
 if (fillCircle) {
  ctx.fill();
 } else {
  ctx.stroke();
 }
};

var drawBee = function (x, y) {
 ctx.lineWidth = 2;
 ctx.strokeStyle = "Black";
 ctx.fillStyle = "Gold";
 circle(x, y, 8, true);
 circle(x, y, 8, false);
 circle(x - 5, y - 11, 5, false);
 circle(x + 5, y - 11, 5, false);
 circle(x - 2, y - 1, 2, false);
 circle(x + 2, y - 1, 2, false);
};

var update = function (coordinate) {
 var offset = Math.random() * 4 - 2;
 coordinate += offset;
 if (coordinate > 200) {
  coordinate = 200;
 }
 if (coordinate < 0) {
  coordinate = 0;
 }
  return coordinate;
};

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var x = 100;
var y = 100;

setInterval(function () {
 ctx.clearRect(0, 0, 200, 200);
 drawBee(x, y);
 x = update(x);
 y = update(y);
 ctx.strokeRect(0, 0, 200, 200);
}, 30);
</script>

Epoch Timestamp

if (!Date.now) {
    Date.now = function() { return new Date().getTime(); }
}

References:

Examples

Dim Image

this.style.opacity=0.6

        function dimImage(tagid) {
            var img = document.getElementById(tagid);
            img.style.opacity = 0.6;
        }

        function undimImage(tagid) {
            var img = document.getElementById(tagid);
            img.style.opacity = 1;
        }

References:


keywords

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