Thanks Corion.

Sorry, the view part is using the inbuilt "alert" function of Javascript. This is what I see of the json string from perl passed to Javascript using "alert":

{ "hex_code":"\\xa5" }
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When I display this in an html input field, it displays:

\xa5
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After much googling with the right keywords, I found a solution by passing the value "\\xa5" (which originates from perl) to the function below:

//https://stackoverflow.com/questions/4209104/decoding-hex-string-in-j
+avascript
String.prototype.decodeEscapeSequence = function() {
    return this.replace(/\\x([0-9A-Fa-f]{4})/g, function() {
        return String.fromCharCode(parseInt(arguments[1], 16));
    });
};
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I think it's somewhat similar to your perl code below:

sub unescape {
    my( $str ) = @_;
    $str =~ s!\\x\{([0-9a-f]{4})\}!chr(hex $1)!ge;
    $str
};
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I am confused because when I have a variable set to a hex value in Javascript like this:

var hex_code = '\xa5';
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That gets displayed correctly in the input field as a symbol.

So I thought since "\\xa5" is what I see with Javascript's alert, if I remove the first backslash, it would work. It doesn't whether I remove the first backslash or not. I needed to unescape with the Javascript function found in stackoverflow.