Substring with reverse index

How can I extract "456" from "xxx_456" where xxx is of indefinite length?

11 Answers

slice works just fine in IE and other browsers, it's part of the specification and it's the most efficient method too:

alert("xxx_456".slice(-3)); //-> 456 

slice Method (String) - MSDN
slice - Mozilla Developer Center

 var str = "xxx_456"; var str_sub = str.substr(str.lastIndexOf("_")+1); 

If it is not always three digits at the end (and seperated by an underscore). If the end delimiter is not always an underscore, then you could use regex:

 var pat = /([0-9]{1,})$/; var m = str.match(pat); 

The substring method allows you to specify start and end index:

var str = "xxx_456"; var subStr = str.substring(str.length - 3, str.length); 

you can just split it up and get the last element

var string="xxx_456"; var a=string.split("_"); alert(a[1]); #or a.pop 

alert("xxxxxxxxxxx_456".substr(-3)) 

caveat: according to mdc, not IE compatible

Simple regex for any number of digits at the end of a string:

'xxx_456'.match(/\d+$/)[0]; //456 'xxx_4567890'.match(/\d+$/)[0]; //4567890 

or use split/pop indeed:

('yyy_xxx_45678901').split(/_/).pop(); //45678901 

String.prototype.reverse( ) { return Array.prototype.slice.call(this) .reverse() .join() .replace(/,/g,'') } 

using a reverse string method

var str = "xxx_456" str = str.reverse() // 654_xxx str = str.substring(0,3) // 654 str = str.reverse() //456 

if your reverse method returns the string then chain the methods for a cleaner solution.

A crazy regex approach

"xxx_456".match(/...$/)[0] //456 

here is my custom function

function reverse_substring(str,from,to){ var temp=""; var i=0; var pos = 0; var append; for(i=str.length-1;i>=0;i--){ //alert("inside loop " + str[i]); if(pos == from){ append=true; } if(pos == to){ append=false; break; } if(append){ temp = str[i] + temp; } pos++; } alert("bottom loop " + temp); } var str = "bala_123"; reverse_substring(str,0,3); 

This function works for reverse index.

Also you can get the result by using substring and lastIndexOf -

alert("xxx_456".substring("xxx_456".lastIndexOf("_")+1)); 

Although this is an old question, to support answer by user187291

In case of fixed length of desired substring I would use substr() with negative argument for its short and readable syntax

"xxx_456".substr(-3) 

For now it is compatible with common browsers and not yet strictly deprecated.