function getSource(fn) {
      var result = '';
      if (isStringable(fn)) {
        result = String(fn);
      } else if (support.decompilation) {
        // Escape the `{` for Firefox 1.
        result = _.result(/^[^{]+\{([\s\S]*)\}\s*$/.exec(fn), 1);
      }
      // Trim string.
      result = (result || '').replace(/^\s+|\s+$/g, '');

      // Detect strings containing only the "use strict" directive.
      return /^(?:\/\*+[\w\W]*?\*\/|\/\/.*?[\n\r\u2028\u2029]|\s)*(["'])use strict\1;?$/.test(result)
        ? ''
        : result;
    }
Gets the source code of a function.

@private
@param {Function} fn The function.
@returns {string} The function's source code.