jQuery Core Method Extend

jQuery Core
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jQuery.extend = jQuery.fn.extend = function() {
  var options, name, src, copy, copyIsArray, clone,
      target = arguments[0] || {},
      i = 1,
      length = arguments.length,
      deep = false;

  // Handle a deep copy situation
  if ( typeof target === "boolean" ) {
      deep = target;
      target = arguments[1] || {};
      // skip the boolean and the target
      i = 2;
  }

  // Handle case when target is a string or something (possible in deep copy)
  if ( typeof target !== "object" && !jQuery.isFunction(target) ) {
      target = {};
  }

  // extend jQuery itself if only one argument is passed
  if ( length === i ) {
      target = this;
      --i;
  }

  for ( ; i < length; i++ ) {
      // Only deal with non-null/undefined values
      if ( (options = arguments[ i ]) != null ) {
          // Extend the base object
          for ( name in options ) {
              src = target[ name ];
              copy = options[ name ];

              // Prevent never-ending loop
              if ( target === copy ) {
                  continue;
              }

              // Recurse if we're merging plain objects or arrays
              if ( deep && copy && ( jQuery.isPlainObject(copy) || (copyIsArray = jQuery.isArray(copy)) ) ) {
                  if ( copyIsArray ) {
                      copyIsArray = false;
                      clone = src && jQuery.isArray(src) ? src : [];

                  } else {
                      clone = src && jQuery.isPlainObject(src) ? src : {};
                  }

                  // Never move original objects, clone them
                  target[ name ] = jQuery.extend( deep, clone, copy );

              // Don't bring in undefined values
              } else if ( copy !== undefined ) {
                  target[ name ] = copy;
              }
          }
      }
  }

  // Return the modified object
  return target;
};

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