Difference between string.indexOf() and string.lastIndexOf()? [closed]

Question

What's the difference between string.indexOf() and string.lastIndexOf() in JavaScript?

var temp = state.indexOf("tmp");    
var temp = state.lastIndexOf("tmp");

Answer 1

From MDN :

The indexOf() method returns the index within the calling String object of the first occurrence of the specified value, The lastIndexOf() method returns the index within the calling String object of the last occurrence of the specified value

So the indexOf will return first occurrence of the value and the lastIndexOf will return the last occurence of the value.

Example (copied from MDN):

var anyString = "Brave new world";
var a = anyString.indexOf("w")); // result = 8
var b = anyString.lastIndexOf("w")); // result 10

Both of the method return -1 if the value is not found

More :

• indexOf
• lastIndexOf

Answer 2

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

string.lastIndexOf() method returns the position of the last occurrence of a specified value in a string.

Answer 3

indexOf() function is match first occurance, LastindexOf() function is match last occurance

Both function are using for finding index in String or Array;

sample code with String operation

var state = "abcdtmpefgtmp";
var temp =state.indexOf("tmp"); //match first occurance
console.log(temp);
//>4

var temp =state.lastIndexOf("tmp"); //match last occurance
console.log(temp);
//>10

sample code with Array operation

var state = ["abc", "tmp", "efg", "tmp"];
var temp =state.indexOf("tmp");
console.log(temp);
//>1
var temp = state.lastIndexOf("tmp");
console.log(temp);
//>3

Answer 4

The lastIndexOf() method returns the position of the last occurrence of a specified value in a string, where as indexOf() returns the position of the first occurrence of a specified value in a string.

In the following example:

 function myFunction() {
     var str = "Hello planet earth, you are a great planet.";
     var n = str.lastIndexOf("planet");
     var n2 = str.indexOf("planet");

 }

n will return 36 and n2 will return 6

Please let me know if you have any questions!