lastIndexOf ()
Javascript array lastIndexOf() method returns the last
index at which a given element can be found in the array, or -1 if it is not
present. The array is searched backwards, starting at fromIndex.
Syntax
Its syntax is as follows:
array.join(separator);
Parameter Details
·
searchElement : Element to locate in the array.
· fromIndex : The index at which to
start searching backwards. Defaults to the
array's length, i.e., the whole array will be searched. If the index is greater
than or equal to the length of the array, the whole array will be searched. If
negative, it is taken as the offset from the end of the array.
Return Value
Returns the index of the found element from the last.
Compatibility
This method is a
JavaScript extension to the ECMA-262 standard; as such it may not be present in
other implementations of the standard. To make it work, you need to add the
following code at the top of your script.
if (!Array.prototype.lastIndexOf)
{
Array.prototype.lastIndexOf = function(elt /*,
from*/)
{
var len = this.length;
var from = Number(arguments[1]);
if (isNaN(from))
{
from = len - 1;
}
else
{
from = (from < 0)
? Math.ceil(from)
: Math.floor(from);
if (from < 0)
from += len;
else if (from >= len)
from = len - 1;
}
for (; from > -1; from--)
{
if (from in this &&
this[from] === elt)
return from;
}
return -1;
};
}
Example
Try the following example.
<html>
<head>
<title>JavaScript Array lastIndexOf
Method</title>
</head>
<body>
<script
type="text/javascript">
if (!Array.prototype.lastIndexOf)
{
Array.prototype.lastIndexOf = function(elt
/*, from*/)
{
var len = this.length;
var from = Number(arguments[1]);
if (isNaN(from))
{
from = len - 1;
}
else
{
from = (from < 0)
? Math.ceil(from)
: Math.floor(from);
if (from < 0)
from += len;
else if (from >= len)
from = len - 1;
}
for (; from > -1; from--)
{
if (from in this &&
this[from] === elt)
return from;
}
return -1;
};
}
var index = [12, 5, 8, 130,
44].lastIndexOf(8); document.write("index is : " + index );
var index = [12, 5, 8, 130, 44,
5].lastIndexOf(5);
document.write("<br />index is :
" + index );
</script>
</body>
</html>
Output
index is : 2
index is : 5
map ()
Javascript array map() method creates a new array with the results of calling a
provided function on every element in this array.
Syntax
Its syntax is as follows:
array.map(callback[, thisObject]);
Parameter Details
·
callback : Function that
produces an element of the new Array from an element of the current one.
·
thisObject : Object to use as this when
executing callback.
Return Value
Returns the created array.
Compatibility
This method is a JavaScript
extension to the ECMA-262 standard; as such it may not be present in other
implementations of the standard. To make it work, you need to add the following
code at the top of your script.
if (!Array.prototype.map)
{
Array.prototype.map = function(fun /*,
thisp*/)
{
var len = this.length;
if (typeof fun != "function")
throw new TypeError();
var res = new Array(len);
var thisp = arguments[1];
for (var i = 0; i < len; i++)
{
if (i in this)
res[i] = fun.call(thisp, this[i], i, this);
}
return res;
};
}
Example
Try the following example.
<html>
<head>
<title>JavaScript Array map
Method</title>
</head>
<body>
<script
type="text/javascript">
if (!Array.prototype.map)
{
Array.prototype.map = function(fun /*,
thisp*/)
{
var len = this.length;
if (typeof fun != "function")
throw new TypeError();
var res = new Array(len);
var thisp = arguments[1];
for (var i = 0; i < len; i++)
{
if (i in this)
res[i] = fun.call(thisp, this[i], i, this);
}
return res;
};
}
var numbers = [1, 4, 9];
var roots = numbers.map(Math.sqrt);
document.write("roots is : " +
roots );
</script>
</body>
</html>
Output
roots is : 1,2,3
pop ()
Javascript array pop() method removes the last element from an array and returns
that element.
Syntax
Its syntax is as follows:
Array.pop();
Return Value
Returns the removed element from the array.
Example
Try the following example.
<html>
<head>
<title>JavaScript Array pop
Method</title>
</head>
<body>
<script
type="text/javascript">
var numbers = [1, 4, 9];
var element = numbers.pop();
document.write("element is : " + element );
var element = numbers.pop();
document.write("<br />element is :
" + element );
</script>
</body>
</html>
Output
element is : 9
element is : 4
push ()
Javascript array push() method appends the given element(s) in the last of the array
and returns the length of the new array.
Syntax
Its syntax is as follows:
Array.push();
Parameter Details
element1, ...,
elementN: The
elements to add to the end of the array.
Return Value
Returns the length of the new array.
Example
Try the following example.
<html>
<head>
<title>JavaScript Array push
Method</title>
</head>
<body>
<script
type="text/javascript">
var numbers = new Array(1, 4, 9);
var length = numbers.push(10);
document.write("new numbers is : " + numbers );
length = numbers.push(20);
document.write("<br />new numbers
is : " + numbers );
</script>
</body>
</html>
Output
new numbers is : 1,4,9,10
new numbers is : 1,4,9,10,20
reduce ()
Javascript array reduce() method applies a function simultaneously against two
values of the array (from left-to-right) as to reduce it to a single value.
Syntax
Its syntax is as follows:
array.reduce(callback[, initialValue]);
Parameter Details
·
callback : Function to execute on each value in the array.
·
initialValue : Object to use as the
first argument to the first call of the callback.
Return Value
Returns the reduced single value of the array.
Compatibility
This method is a
JavaScript extension to the ECMA-262 standard; as such it may not be present in
other implementations of the standard. To make it work, you need to add the
following code at the top of your script.
if (!Array.prototype.reduce)
{
Array.prototype.reduce = function(fun /*,
initial*/)
{
var len = this.length;
if (typeof fun != "function")
throw new TypeError();
// no value to return if no initial value
and an empty array if (len == 0 && arguments.length == 1)
throw new TypeError();
var i = 0;
if (arguments.length >= 2)
{
var rv = arguments[1];
}
else
{
do
{
if (i in this)
{
rv = this[i++];
break;
}
// if array contains no values, no
initial value to return if (++i >= len)
throw new TypeError();
}
while (true);
}
for (; i < len; i++)
{
if (i in this)
rv = fun.call(null, rv, this[i], i, this);
}
return rv;
};
}
Example
Try the following example.
<html>
<head>
<title>JavaScript Array reduce
Method</title>
</head>
<body>
<script
type="text/javascript">
if (!Array.prototype.reduce)
{
Array.prototype.reduce = function(fun /*,
initial*/)
{
var len = this.length;
if (typeof fun != "function")
throw new TypeError();
// no value to return if no initial
value and an empty array if (len == 0 && arguments.length == 1)
throw new TypeError();
var i = 0;
if (arguments.length >= 2)
{
var rv = arguments[1];
}
else
{
do
{
if (i in this)
{
rv = this[i++];
break;
}
// if array contains no values, no
initial value to return if (++i >= len)
throw new TypeError();
}
while (true);
}
for (; i < len; i++)
{
if (i in this)
rv = fun.call(null, rv, this[i], i, this);
}
return rv;
};
}
var total = [0, 1, 2,
3].reduce(function(a, b){ return a + b; }); document.write("total is :
" + total ); </script>
</body>
</html>
Output
total is : 6
reduceRight ()
Javascript array reduceRight() method applies a function
simultaneously against two values of the array (from right-to-left) as to
reduce it to a single value.
Syntax
Its syntax is as follows:
array.reduceRight(callback[, initialValue]);
Parameter Details
·
callback : Function to execute on each value in the array.
·
initialValue : Object to use as the
first argument to the first call of the callback.
Return Value
Returns the reduced right single value of the array.
Compatibility
This method is a
JavaScript extension to the ECMA-262 standard; as such it may not be present in
other implementations of the standard. To make it work, you need to add the
following code at the top of your script.
if (!Array.prototype.reduceRight)
{
Array.prototype.reduceRight = function(fun
/*, initial*/)
{
var len = this.length;
if (typeof fun != "function")
throw new TypeError();
// no value to return if no initial
value, empty array if (len == 0 && arguments.length == 1)
throw new TypeError();
var i = len - 1;
if (arguments.length >= 2)
{
var rv = arguments[1];
}
else
{
do
{
if (i in this)
{
rv = this[i--];
break;
}
// if array contains no values, no
initial value to return if (--i < 0)
throw new TypeError();
}
while (true);
}
for (; i >= 0; i--)
{
if (i in this)
rv = fun.call(null, rv, this[i], i, this);
}
return rv;
};
}
Example
Try the following example.
<html>
<head>
<title>JavaScript Array reduceRight
Method</title>
</head>
<body>
<script type="text/javascript">
if (!Array.prototype.reduceRight)
{
Array.prototype.reduceRight = function(fun
/*, initial*/)
{
var len = this.length;
if (typeof fun != "function")
throw new TypeError();
// no value to return if no initial
value, empty array if (len == 0 && arguments.length == 1)
throw new TypeError();
var i = len - 1;
if (arguments.length >= 2)
{
var rv = arguments[1];
}
else
{
do
{
if (i in this)
{
rv = this[i--];
break;
}
// if array contains no values, no
initial value to return if (--i < 0)
throw new TypeError();
}
while (true);
}
for (; i >= 0; i--)
{
if (i in this)
rv = fun.call(null, rv, this[i], i, this);
}
return rv;
};
}
var total = [0, 1, 2,
3].reduceRight(function(a, b){ return a + b; }); document.write("total is
: " + total ); </script>
</body>
</html>
Output
total is : 6
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