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JavaScript JavaScript Loops, Arrays and Objects Tracking Multiple Items with Arrays Useful Array Methods

Hugo M
Hugo M
4,517 Points
Posted by Hugo M
Hugo M
4,517 Points

What if a string is in the array more than once?

Hi guys, I was wondering what you'd have to do if the string was in the array more than once? Say apple was at position 0 and again at 5.

The indexOf function gives up after if finds the first instance. The only way I can think of doing it is by looping the function until it returns -1. Thereby returning all the instances of apple. Is there an easier way?

3 Answers

William Li
PLUS
William Li
Courses Plus Student 26,868 Points
William Li
William Li
Courses Plus Student 26,868 Points

Hi, Hugo. The complete syntax of the indexOf() method is string.indexOf(searchValue, startingIndex), the 2nd argument startingIndex is optional, by default, if you don't pass in the 2nd argument to indexOf() method call, it starts its search from the beginning of the String, and return the first occurrence of the search value.

If there're multiple occurrences of the search value in a String, and you'd like to catch them all. You can just write a loop, find the first occurrences of the word using string.indexOf(searchValue), then continue the search by calling string.indexOf(searchValue, foundIndex + 1) until it eventually exhausts all the possible occurrences of the search value in the given string and returns -1.

Christian Weatherford
Christian Weatherford
8,848 Points
Christian Weatherford
Christian Weatherford
8,848 Points

You're right that looping is the best option, but simply calling array.indexOf("apple") will just give you the the first occurrence over and over. You'll want to use the form of the indexOf method that takes a starting point as well. So something like:

var array = [/*contents of array*/];
var searchString = "apple";
var index = -1;

do {
  index = array.indexOf(searchString, index + 1);
  if (index !== -1) {
    console.log("The string " + searchString + " was found at index " + index);
  }
} while (index !== -1);