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The replace function returns the new string with the replaces, but if there weren't any words to replace, then the original string is returned. Is there a way to know whether it actually replaced anything apart from comparing the result with the original string?
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The String type provides you with the replace() and replaceAll() methods that allow you to replace all occurrences of a substring in a string and return the new version of the string.
The replace() method searches a string for a specified character, and returns a new string where the specified character(s) are replaced.
The replace() method searches a string for a value or a regular expression. The replace() method returns a new string with the value(s) replaced. The replace() method does not change the original string.
The JavaScript String replace() method returns a new string with a substring ( substr ) replaced by a new one ( newSubstr ). Note that the replace() method doesn't change the original string. It returns a new string.
A simple option is to check for matches before you replace:
var regex = /i/g; var newStr = str; var replaced = str.search(regex) >= 0; if(replaced){ newStr = newStr.replace(regex, '!'); } If you don't want that either, you can abuse the replace callback to achieve that in a single pass:
var replaced = false; var newStr = str.replace(/i/g, function(token){replaced = true; return '!';}); Comparing the before and after strings is the easiest way to check if it did anything, there's no intrinsic support in String.replace().
[contrived example of how '==' might fail deleted because it was wrong]
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