- Categories: JavaScript Methods, JavaScript Reference, Reference
Quick Reference
The Array lastIndexOf() method returns the last position of a specified value, searching from right to left, and returning -1 if the value is not found.
<!-- html element to place output -->
<p id='my_cars'></p>
// array
let cars = ['Maserati', 'Ferrari', 'Maserati', 'Alfa Romeo'];
// find the key of the last occurence of Maserati
let my_index = cars.lastIndexOf('Maserati');
// cycle through the keys and output the last occurence to the HTML element
document.getElementById('my_cars').innerHTML = my_index;
The way this works (see Syntax section below):
- The lastIndexOf() method cycles through the array starting from the end looking for the index of a specified value
Output
2
Syntax
array.lastIndexOf(item, start)
Parameters
| Parameter | Description |
|---|---|
| item | The value to search for (required) |
| start | Where to start the search; negative start values counts from the last element searching from right to left (default array.length-1) |
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JAVASCRIPT NOTES:
- When using JavaScript, single or double quotation marks are acceptable and work identically to one another; choose whichever you prefer, and stay consistent
- JavaScript is a case-sensitive language; firstName is NOT the same as firstname
- Arrays count starting from zero NOT one; so item 1 is position [0], item 2 is position [1], and item 3 is position [2] … and so on
- JavaScript variables must begin with a letter, $, or _
- JavaScript variables are case sensitive (x is not the same as X)
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