14922 java script built (1)

JavaScript Built-in objects
JavaScript supports a number of built-in objects that extend the flexibility of the language. These objects
are Date, Math, String, Array, and Object.
1. String Objects :
<html>
<body>
<p id="demo"></p>
<script>
var carName1 = "Volvo XC60";
var carName2 = 'Volvo XC60';
var answer1 = "It's alright";
var answer2 = "He is called 'Johnny'";
var answer3 = 'He is called "Johnny"';
document.getElementById("demo").innerHTML =
carName1 + "<br>" +
carName2 + "<br>" +
answer1 + "<br>" +
answer2 + "<br>" +
answer3;
</script></body></html>
2. String Length:
<html><body>
<p id="demo"></p>
<script>
var txt="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
document.getElementById("demo").innerHTML = txt.length;
3. Strings can be Objects
 Normally, JavaScript strings are primitive values, created from literals: var firstName =
"John"
 But strings can also be defined as objects with the keyword new: var firstName = new
String("John")
<html><body>

<p id="demo"></p>
<script>
var x = "John"; // x is a string
var y = new String("John"); // y is an object
document.getElementById("demo").innerHTML = typeof x + " " + typeof y;
</script>
</body></html>
JavaScript string methods
4. The slice() Method
 Slice() extracts a part of a string and returns the extracted part in a new string.
 The method takes 2 parameters: the starting index (position), and the ending index
(position).
 This example slices out a portion of a string from position 7 to position 13:
<html><body>
<p>The slice() method extract a part of a string and returns the extracted parts in a new
string:</p>
<p id="demo"></p>
<script>
var str = "Apple, Banana, Kiwi";
document.getElementById("demo").innerHTML = str.slice(7,13);
If a parameter is negative, the position is counted from the end of the string.
5. This example slices out a portion of a string from position -12 to position -6:
<html><body>
string:</p>
<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML = str.slice(-12,-6);

6.If you omit the second parameter, the method will slice out the rest of the sting:
<html><body>
string:</p>
<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML = str.slice(7);
</script>
</body></html>
7. or, counting from the end :
<html><body>
string:</p>
<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML = str.slice(-12);
8. The substring() Method
 Substring () is similar to slice ().
 The difference is that substring () cannot accept negative indexes.
<html><body>
<p>The substr() method extract a part of a string and returns the extracted parts in a
new string:</p>
<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML = str.substring(7,13);

9. The substr() Method
 substr() is similar to slice().
 The difference is that the second parameter specifies the length of the extracted part.
<html><body>
<p>The substr() method extract a part of a string and returns the extracted parts in a
new string:</p>
<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML = str.substr(7,6);
 If the first parameter is negative, the position counts from the end of the string.
 The second parameter can not be negative, because it defines the length.
 If you omit the second parameter, substr() will slice out the rest of the string.
10. Replacing String Content
 The replace() method replaces a specified value with another value in a string:
<html><body>
<p>Replace "Microsoft" with "W3Schools" in the paragraph below:</p>
<button onclick="myFunction()">Try it</button>
<p id="demo">Please visit Microsoft!</p>
<script>
function myFunction() {
var str = document.getElementById("demo").innerHTML;
var txt = str.replace("Microsoft","W3Schools");
document.getElementById("demo").innerHTML = txt;
}
11. Converting to Upper and Lower Case
A string is converted to upper case with toUpperCase():
<html><body>

<p>Convert string to upper case:</p>
<p id="demo">Hello World!</p>
<script>
var text = document.getElementById("demo").innerHTML;
document.getElementById("demo").innerHTML = text.toUpperCase();
}
A string is converted to lower case with toLowerCase():
12. The concat() Method
 concat() joins two or more strings:
<html><body>
<p>The concat() method joins two or more strings:</p>
<p id="demo"></p>
<script>
var text1 = "Hello";
var text2 = "World!"
document.getElementById("demo").innerHTML = text1.concat(" ",text2);
 The concat() method can be used instead of the plus operator. These two lines do the same:
var text = "Hello" + " " + "World!";
var text = "Hello".concat(" ","World!");
13. Extracting String Characters
· charAt(position)
The charAt() Method
 The charAt() method returns the character at a specified index (position) in a string:
<html><body>
<p>The charAt() method returns the character at a given position in a string:</p>
<p id="demo"></p>

<p id="demo"></p>
<script>
var d = new Date("October 13, 2014 11:13:00");
17. Using new Date(), with 7 numbers, creates a new date object with the
specified date and time: The 7 numbers specify the year, month, day, hour, minute,
second, and millisecond, in that order:
<html><body>
<p id="demo"></p>
<script>
var d = new Date(99,5,24,11,33,30,0);
18. Math Functions:
 The Math object allows you to perform mathematical tasks.
 One common use of the Math object is to create a random number:
<html><body>
<p>Math.random() returns a random number betwween 0 and 1.</p>
<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML = Math.random();
}
19. Math.min() and Math.max()
Math.min() can be used to find the lowest value in a list of arguments.
<html><body>
<p>Math.min() returns the lowest value.</p>

<p id="demo"></p>
<script>
Math.min(0, 150, 30, 20, -8);
}
20. Math.max() can be used to find the highest value in a list of arguments.
<html>
<body>
<p>Math.max() returns the higest value.</p>
<p id="demo"></p>
<script>
Math.max(0, 150, 30, 20, -8);
}
21. Math.round(): rounds a number to the nearest
integer
<html><body>
<p>Math.round() rounds a number to its nearest integer.</p>
<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML = Math.round(4.4);
}
22. Math.floor(): rounds a number down to the nearest
integer:
<html><body>
<p>Math.floor() rounds a number <strong>down</strong> to its nearest integer.</p>

<p id="demo"></p>
<script>
document.getElementById("demo").innerHTML = Math.floor(4.7);
}
23. Math Constants
JavaScript provides 3 mathematical constants that can be accessed with the Math object:
<html>
<body>
<p>Math constants are E, PI, SQR2, SQR1_2, LN2, LN10, LOG2E, LOG10E</p>
<p id="demo"></p>
<script>
Math.E + "<br>" +
Math.PI + "<br>" +
Math.SQRT2 + "<br>" ;
}

14922 java script built (1)

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