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How to use lastIndexOf method

不言Original: 2019-02-20 16:05:238221browse

lastIndexOf() method can return the last occurrence position of a specified string value. If the second parameter start is specified, the specified position in a string will be searched from back to front. Let's take a closer look at how to use the lastIndexOf method.

Let’s first take a look at the basic syntax of lastIndexOf()

arr.lastIndexOf(searchElement[,index])

The first parameter of lastIndexOf() is searchElement. It is the value to search for in the array. The second parameter is the optional index, which defines the starting index in the array from which to search for elements backwards. If this parameter is not provided, index arr.length - is used as the starting index to start searching backwards, as it is the default value.

lastIndexOf() returns the index of the last occurrence of searchElement. If the element is not found in the array, this function returns -1.

Let’s look at a specific example

The function lastindexof() returns the last index where 2 appears, which is 0.

The code is as follows

<!DOCTYPE html>
<html>
<head>
  <title></title>
</head>
<body>
<script> 
function func() { 
    var array = [2, 9, 9]; 
    document.write(array.lastIndexOf(2)); 
} 
func(); 
</script> 
</body>
</html>

Output result For: 0

The function lastindexof() finds the last occurrence of index 45. Because it doesn't exist, the function returns -1.

The code is as follows

<!DOCTYPE html>
<html>
<head>
  <title></title>
</head>
<body>
<script> 
function func() { 
    var array = [2, 98, 12, 45]; 
    document.write(array.lastIndexOf(45,2)); 
} 
  
func(); 
</script>
</body>
</html>

The output result is: -1.

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