Apperently, you want to convert halfwidth and fullwidth form characters to their equivalent basic latin forms. If this is correct, you can do a replacement using a regular expression. Something like this should work:
var x = "!abc ABC!";
var y = x.replace(
/[uff01-uff5e]/g,
function(ch) { return String.fromCharCode(ch.charCodeAt(0) - 0xfee0); }
);
Where x is your input string and y is the output.
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