Indexof Redhead
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Indexof Redhead
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arr . indexOf ( searchElement [ , fromIndex ] )
searchElement
Element to locate in the array.
fromIndex Optional
The index to start the search at. If the index is greater than or equal to the
array's length, -1 is returned, which means the array will not be searched. If the
provided index value is a negative number, it is taken as the offset from the end of
the array. Note: if the provided index is negative, the array is still searched from
front to back. If the provided index is 0, then the whole array will be searched.
Default: 0 (entire array is searched).
var indices = [ ] ;
var array = [ 'a' , 'b' , 'a' , 'c' , 'a' , 'd' ] ;
var element = 'a' ;
var idx = array . indexOf ( element ) ;
while ( idx != - 1 ) {
indices . push ( idx ) ;
idx = array . indexOf ( element , idx + 1 ) ;
}
console . log ( indices ) ;
// [0, 2, 4]
function updateVegetablesCollection ( veggies , veggie ) {
if ( veggies . indexOf ( veggie ) === - 1 ) {
veggies . push ( veggie ) ;
console . log ( 'New veggies collection is : ' + veggies ) ;
} else if ( veggies . indexOf ( veggie ) > - 1 ) {
console . log ( veggie + ' already exists in the veggies collection.' ) ;
}
}
var veggies = [ 'potato' , 'tomato' , 'chillies' , 'green-pepper' ] ;
updateVegetablesCollection ( veggies , 'spinach' ) ;
// New veggies collection is : potato,tomato,chillies,green-pepper,spinach
updateVegetablesCollection ( veggies , 'spinach' ) ;
// spinach already exists in the veggies collection.
The indexOf() method returns the first index at which a
given element can be found in the array, or -1 if it is not present.
The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.
The first index of the element in the array; -1 if not found.
indexOf() compares searchElement to elements of
the Array using strict
equality (the same method used by the === or triple-equals operator).
Note: For the String method, see
String.prototype.indexOf() .
The following example uses indexOf() to locate values in an array.
indexOf() was added to the ECMA-262 standard in the 5th edition; as such
it may not be present in all browsers. You can work around this by utilizing the
following code at the beginning of your scripts. This will allow you to use
indexOf() when there is still no native support. This algorithm matches the
one specified in ECMA-262, 5th edition, assuming TypeError and Math.abs() have their original values.
However, if you are more interested in all the little technical bits defined by the
ECMA standard, and are less concerned about performance or conciseness, then you may
find this more descriptive polyfill to be more useful.
BCD tables only load in the browser
Last modified: Feb 19, 2021 , by MDN contributors
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JavaScript String indexOf () Method
Array.prototype. indexOf () - JavaScript | MDN
JavaScript String indexOf () Explained By Practical Examples
String. IndexOf Method (System) | Microsoft Docs
Groovy - indexOf () - Tutorialspoint
Home / JavaScript Tutorial / JavaScript String indexOf()
The JavaScript Tutorial website helps you learn JavaScript programming from scratch quickly and effectively.
Summary : in this tutorial, you’ll learn how to use the JavaScript String indexOf() method to find the index of a substring within a string.
The String.prototype.indexOf() returns the index of the first occurrence of substring ( substr ) in a string ( str ):
It returns -1 if the str does not contain the substr .
The fromIndex is an optional parameter that specifies the index at which the search starts. It defaults to zero (0), meaning that if you omit the fromIndex , the search will start from the beginning of the string.
The indexOf() always perform a case-sensitive search.
To find the index of the last occurrence of a substring in a string, you use the lastIndexOf() method.
Let’s take some examples of using the indexOf() method.
The following example uses the indexOf() to get the index of the first occurrence of the substring 'str' in the string 'finding substring in string' :
The following example uses the indexOf() method to count the number of occurrences of the substring 'know' in the string 'You do not know what you do not know until you know.' :
The indexOf() is case-sensitive. See the following example:
In this example, the indexOf() returns -1 because the string JS IndexOf does not contain the substring js but JS .
To perform a case-insensitive search for the index of a substring within a string, you can convert both substring and string to lowercase before using the indexOf() method as follows:
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