jQuery extend 的简单实例

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;
};