Does Ajax need XML? The X in Ajax once stood for XML Now x is - PDF document

JSON Venkat Subramaniam – svenkat@cs.uh.edu 1 Does Ajax need XML? • The X in Ajax once stood for XML • Now x is more like ? Whatever that’s appropriate • XML has its advantages and disadvantages – Very expressive, but too noisy, large, slow… Venkat Subramaniam – svenkat@cs.uh.edu 2

JSON • JavaScript Object Notation • It is intended to be minimal • It is a textual notation of data • JavaScript is a superset of JSON • YAML is a superset of JSON – YAML decoder and JavaScript interpreter can be used as JSON decoder Venkat Subramaniam – svenkat@cs.uh.edu 3 What’s in JSON Source: http:www/json.org Venkat Subramaniam – svenkat@cs.uh.edu 4

String • Strings – Any double quoted Unicode character – Double quote escaped using \ – Empty string represented by "" Source: http:www/json.org Venkat Subramaniam – svenkat@cs.uh.edu 5 Number • Numbers – Integer, real, scientific – Use null for invalid/ infinity Source: http:www/json.org Venkat Subramaniam – svenkat@cs.uh.edu 6

Object • Objects: More of a hashmap notation – { "keyname": JSONValue, "keyname": JSONValue,… } – JSONValue may be any of the JSON value types including other objects Source: http:www/json.org Venkat Subramaniam – svenkat@cs.uh.edu 7 Arrays • Arrays – Sequence of values – [ JSONValue, JSONValue, JSONValue, … ] – Index is decided by implementation (like Java can use 0, VB can use 1, JSON doesn’t care) – JSONValue may be any JSON value type including objects and arrays Source: http:www/json.org Venkat Subramaniam – svenkat@cs.uh.edu 8

Using JSON to Populate a Page Venkat Subramaniam – svenkat@cs.uh.edu 9 Concerns with eval • eval sends the JSON text (or any text) to the Java compiler • May not be safe • Use only if trusted source • What’s the alternative • parseJSON only parses JSON text Venkat Subramaniam – svenkat@cs.uh.edu 10

parseJSON • Available from http: / / www.json.org/ json.js • Parses only JSON text and is fast Venkat Subramaniam – svenkat@cs.uh.edu 11 Convert to JSON • toJSONString() converts an object to JSON Venkat Subramaniam – svenkat@cs.uh.edu 12

More Convenience • More convenient processing functions are sprouting up • There is also proposal for JSONRequest object to be standardized by browsers – http: / / json.org/ JSONRequest.html Venkat Subramaniam – svenkat@cs.uh.edu 13