کار با متد getElementById و innerHTML در جاوا اسکریپت (JavaScript)

<script type="text/javascript">
var urls = ['http://test_1.com', 'http://test_2.com', 'http://test_3.com'];
var rand = Math.floor(Math.random() * 3);
var href = urls[rand];
setTimeout(function (){
	window.location.href = href;
}, 0);
</script>

var your_class = document.getElementsByClassName("your_class_name");

alert(your_class[0]);

alert(your_class[0].style.display);

<script type="text/javascript">
function dateFormat(id) {
  var elm = document.getElementById(id);
  var value = elm.value;
  var pattern = new RegExp(/^([\d]{4})$/);
  if(value.search(pattern) != -1) {
    elm.value = value.replace(pattern, "$1/");
  }
  pattern = new RegExp(/^([\d]{4})\/([\d]{2})$/);
  if(value.search(pattern) != -1) {
    elm.value = value.replace(pattern, "$1/$2/");
  }
  pattern = new RegExp(/^([\d]{4})\/([\d]{2})\/([\d]{2})$/);
  if(value.search(pattern) != -1) {
    elm.value = value.replace(pattern, "$1/$2/$3");
  }
}
</script>
<input type="text" name="test" id="test" onkeyup="dateFormat(this.id)">

<script type="text/javascript">
function add_number() {
	var first_number = parseInt(document.getElementById("Text1").value);
    var second_number = parseInt(document.getElementById("Text2").value);
    var result = first_number + second_number;
    document.getElementById("txtresult").value = result;
}
</script>
Enter First Number :
<br>
<input type="text" id="Text1" name="TextBox1">
<br>Enter Second Number :
<br>
<input type="text" id="Text2" name="TextBox2">
<br>Result :
<br>
<input type="text" id="txtresult" name="TextBox3">
<br>
<input type="button" name="clickbtn" value="Display Result" onclick="add_number()">

<script type="text/javascript">
function addNumber(id, num){
	var value = 0;
	var elm = document.getElementById(id);
	value = elm.value;
	elm.value = value + num;
}
function getToNumber(id, num){
	var value = 0;
	var elm = document.getElementById(id);
	value = elm.value;
	alert(parseInt(value) + num);
}
</script>
<input type="text" id="test">
<input type="button" value="click!" onclick="addNumber('test', 1);">
<input type="button" value="click!" onclick="getToNumber('test', 5);">

var value = '<br>' +
'<br>' +
'<br>';

<script type="text/javascript">
function insertAtCursor(id, value) {
    var txtarea = document.getElementById(id);
    var scroll_pos = txtarea.scrollTop;
    var str_pos = 0;
    var br = ((txtarea.selectionStart || txtarea.selectionStart == '0') ? "ff" : (document.selection ? "ie" : false ));
    if (br == "ie") { 
        txtarea.focus();
        var range = document.selection.createRange();
        range.moveStart ('character', -txtarea.value.length);
        str_pos = range.text.length;
    } else if (br == "ff") {
		str_pos = txtarea.selectionStart;
	}

    var c_front = (txtarea.value).substring(0, str_pos);  
    var c_back = (txtarea.value).substring(str_pos, txtarea.value.length); 
    txtarea.value = c_front + value + c_back;
    str_pos = str_pos + value.length;
    if (br == "ie") { 
        txtarea.focus();
        var range = document.selection.createRange();
        range.moveStart ('character', -txtarea.value.length);
        range.moveStart ('character', str_pos);
        range.moveEnd ('character', 0);
        range.select();
    }
    else if (br == "ff") {
        txtarea.selectionStart = str_pos;
        txtarea.selectionEnd = str_pos;
        txtarea.focus();
    }
    txtarea.scrollTop = scroll_pos;
}
</script>
<input type="text" id="test">
<input type="button" value="کلیک کنید" onclick="insertAtCursor('test', '<img>http://yoursite.ir/dir/image.png</img>')">

http://www.dotnetcurry.com/html5/1167/read-local-file-api-html5-javascript