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JavaScript indexOf() | Get First Index of a Value in an Array
The JavaScript indexOf() method is used to find the first index of a specified value in an array. For example:
<!DOCTYPE html> <html> <body> <p>Index of "UK" = <span id="fresherearth"></span></p> <script> const countries = ["Luxembourg", "USA", "Australia", "UK", "Finland", "Canada"]; let x = countries.indexOf("UK"); document.getElementById("fresherearth").innerHTML = x; </script> </body> </html>
Index of "UK" =
JavaScript indexOf() Syntax
The syntax of indexOf() method in JavaScript is:
array.indexOf(item, startIndex)
The item refers to the item or value or element of which, we need to get the index number. And the startIndex parameter is optional that is used to start searching for specified item from particular index number. For example:
<!DOCTYPE html> <html> <body> <p>Index = <span id="myspan"></span></p> <script> const ctrs = ["Luxembourg", "USA", "Australia", "UK", "USA", "Canada"]; let myi = ctrs.indexOf("USA", 2); document.getElementById("myspan").innerHTML = myi; </script> </body> </html>
Index =
Note - Indexing starts with 0. Therefore Australia is at index number 2.
What if Specified Element is not Available in Given Array?
Let's check it out, what will happen if the specified item is not available in the given array:
<!DOCTYPE html> <html> <body> <p>Index of "UAE" = <span id="myspn"></span></p> <script> const crs = ["Luxembourg", "USA", "Australia", "UK", "USA", "Canada"]; let i = crs.indexOf("UAE", 2); document.getElementById("myspn").innerHTML = i; </script> </body> </html>
Index of "UAE" =
That means, the indexOf() method returns -1 if specified item does not found. Therefore, we can use JavaScript code like this to avoid printing the returned value itself.
<!DOCTYPE html> <html> <body> <script> const c = ["Luxembourg", "USA", "Australia", "UK", "USA", "Canada"]; let nx = c.indexOf("UAE", 2); if(nx == -1) console.log("The country \"UAE\" is not available in the list."); else console.log("Index of \"UAE\" = ", nx); </script> </body> </html>
The snapshot given below shows the sample output produced by above JavaScript example:
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