Spread HTML test page

# Serialization ## Content SpreadJS supports serialization of custom cell types, custom functions, custom formatters, custom tags, and custom sparklineEx. When serialized, a custom type's **toJSON** method stores a string field type that indicates itself. The string type is related to the window, such as `mynamespace.MyCellType`. When deserialized, the **getTypeFromString** method gets the custom type by parsing the type string, then creates an instance of the custom type, and then invokes the **fromJSON** method of the instance. If you assign the actual type string to the type field of a custom type, the custom type is serialized and deserialized. If a custom type has a circular dependency or you want to reduce the JSON size or have some other requirement, the custom type also needs to override the **toJSON** and **fromJSON** methods. If you do not want to put the custom type on a window object, you also need to override the **getTypeFromString** method for parsing the type string. The following code sample uses spread1’s toJSON and spread2’s fromJSON function to implement serializing all data from spread1 to spread2. The `MyTag` instance is on spread2 after selecting the button. ```html Spread HTML test page

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