typeid

Summary

Returns the type of an expression at runtime.

Syntax

typeid expression

Parameters

expression: Any valid expression.

Description

typeid returns the type of an expression at runtime.

typeid is an improved and fixed typeof operator that is compatible with JS++ types. (JS++ inherited from typeof from JavaScript.)

For JS++ Types

For JS++ types, typeid will return the exact type for an expression. Additionally, typeid will return accurate numeric types; for example, 1 + 1 will return "int", whereas typeof will return "number". Likewise, for objects, the class type will be returned.

When auto-boxing, if the wrapper class is declared as the type for a variable, the wrapper class type will be returned for typeid:

System.Boolean b = true;
typeid b; // "System.Boolean"

For JavaScript Types

Unlike JavaScript's typeof operator, the JS++ typeid operator includes fixes, such as typeid null returning "void" instead of "object". The following table describes the values for typeid on external JavaScript values:

Type	Value
Global object	external<global>
boolean	external<boolean>
string	external<string>
number	external<number>
NaN	external<number NaN>
Infinity	external<number Infinity>
function	external<Function>
Arrays	external<Array>
Objects (`{ ... }`)	external<Object>
null	external<void>
undefined	external<void>
Host objects	external<object ...>

Examples

typeid on internal types

import System;
 
int x;
string s;
 
Console.log(typeid x); // "int"
Console.log(typeid s); // "string"

typeid on external types

import System;
import Externals.DOM;
 
var a = [ 1, 2, 3 ];
var b = document.createElement("div");
 
Console.log(typeid x); // "external<Array>"
Console.log(typeid s); // "external<object HTMLDivElement>"