CODEWITHSUNDEEP
javascript
user4932805
user4932805

Reputation:

JavaScript--indexOf Basics

In the following snippet, what role does pos = string.indexOf( 'e', pos + 1 ) play? 

var string = 'To be, or not to be, that is the question';

var count = 0;

var pos = string.indexOf('e');

while ( pos !== -1 ) {
  count++;
  pos = string.indexOf( 'e', pos + 1 )
}

console.log(count);

Upvotes: 0

Views: 80

Answers (4)

Munawir
Munawir

Reputation: 3356

The indexOf() method returns the position of the first occurrence of a specified value in a string.

Syntax :

string.indexOf(searchvalue,start)
  • searchvalue - [Required]. The string to search for
  • start - [Optional]. Default 0. At which position to start the search

Return a Number, representing the position where the specified searchvalue occurs for the first time, or -1 if it never occurs

var str = "To be, or not to be, that is the question";
var n = str.indexOf("e", 5);

The above code returns the first occurrence of the letter "e" in a string, starting the search at position 5:

For more : Click here

Note: The indexOf() method is case sensitive.

Upvotes: 1

André Junges
André Junges

Reputation: 5357

The second parameter of the indexOf function is the index you want to start to look in the string

As you can see in here

str.indexOf(searchValue[, fromIndex])

If you didn't use the secondParam in that case, you would be getting the position of the first 'e' forever. This function is counting the numbers of 'e's in that phrase.

Upvotes: 2

Martin McKeaveney
Martin McKeaveney

Reputation: 508

The second argument in string.indexOf is the index of the string to start searching from.

See here - https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/String/indexOf#Parameters

All this code does is count the number of e's in the sentence.

Upvotes: 1

Akshat Mahajan
Akshat Mahajan

Reputation: 9846

From the docs, indexOf takes an additional parameter:

fromIndex (Optional)

The index at which to start the searching forwards in the string. It can be any integer. The default value is 0, so the whole array is searched. If fromIndex < 0 the entire string is searched. If fromIndex >= str.length, the string is not searched and -1 is returned. Unless searchValue is an empty string, then str.length is returned.

Judging purely from this information, the behaviour of the program as a whole is easily deduced:

  • It counts the number of times e appears in the string overall, using string.indexOf to find each occurence.

string.indexOf only returns the position of the first occurence of the character in the string. By passing and updating fromIndex with the value of pos, string.indexOf finds all subsequent occurences of e by ignoring characters before pos.

A counter is updated each time it does so, allowing the program as a whole to compute the number of times e appears in the string.

Upvotes: 2

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