refactor custom sanitizers

src/boundingbox.js

-const isValid = (value) => {
-
-  let tokens = value.split(",");
-  tokens = tokens.map(token => parseFloat(token));
-  if (tokens[0] < tokens[2] && tokens[1] < tokens[3]) {
-    return true;
-  }
-  return false;
-
-}
-
-module.exports = { isValid };
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