/********************************************************************** * * JavaScript types and objects * * **********************************************************************/ // // Types and objects // ================= // // JavaScript's type system is split into two categories of enteties: // basic types or values and objects, they differ in several aspects. // // | values | objects // ----------------+-------------------+-------------------------- // mutability | imutable | mutable // ----------------+-------------------+-------------------------- // identity | equal values are | different objects // | the same entity | can have same // | (singletons) | structure // ----------------+-------------------+-------------------------- // // // Basic values // ------------ // // numbers var integer = 123 var floating_point = 3.1415 var hex = 0xFF // strings var string = 'string' var another_string = "also a string" var template = ` a template string. this can include \\n's also summorts expansions ${ '.' }` // boolieans var t = true var f = false // nulls var n = null var u = undefined var not_a_number = NaN // Values are in general: // // - singletons var a = 3.14 var b = 3.14 a === b // -> true // In general equal basic values are the same value and there is // no way to create two copies of the same value. // - imutable var a = 1 var b = a // a and b hold the same value (1) a === b // -> true // now we update a... a += 1 a === b // -> false // Note that we updated the value referenced by a, i.e. the old // value (1) was not modified by the addition (b is still 1), // rather a new value (2) was created and assigned to a. // Equality and identity // // Automatic type coercion // // Type checking // typeof(42) // -> 'number' // Objects // ------- // // Type cheking // // Here thesame approach as for simple types is not productive: typeof([42]) // -> 'object' typeof({}) // -> 'object' // so a better approach would be to: [42] instanceof Array // -> true // but since all objects are objects the test can get quite generic (XXX) [42] instanceof Object // -> true {} instanceof Object // -> true // Prototypes and inheritance // // // Constructors // // /********************************************************************** * vim:set ts=4 sw=4 : */