Smart String Replacements

This works well for case insensitive replacements:

str = str.replace(new RegE开发者_如何学JAVAxp(phrase, 'gi'), '<span style="color:red;">' + phrase + '</span>');

But what I do want is to not change case when replaced which above-mentioned does.

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str = str.replace(new RegExp(phrase, 'gi'), '<span>$&</span>');

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Capture the phrase with parenthesis, and use $1 in the replace string, eg:

'Foobar'.replace(/(foo)/gi, '<x>$1</x>')

Would result in <x>Foo</x>bar