Type Conversion

The as operator is used for: conversion between primitive types (including Nullable and variant), down-casting of object types.

The conversion rules between primitive types are defined as follows. If the source type is a Nullable type and if the value is null, a run-time exception is raised under debug builds. The behavior is unspecified for release builds.

The result of conversion from a variant type depends on the result of the typeof operator applied to the variant.

Down-casting of an object type returns a reference to the casted object if successful, otherwise null.

Table 1. Conversion between the Primitive Types using the As Operator
Source Type	Destination Type	Result
boolean	number	0 if false, 1 if true
boolean	int	same as above
boolean	string	"false" if false, "true" if true
number	boolean	false if 0 or NaN, otherwise true
number	int	fractional part is removed, becomes 0 if NaN, may get rounded to between -2³¹ and 2³¹-1
number	string	converted to string representation
int	boolean	false if 0, otherwise true
int	number	converted to number of same value
int	string	converted to string representation
string	boolean	false if the string is empty, otherwise true
string	number	0 if the string is empty, a number if the string can be parsed as a string, otherwise NaN
string	int	equivalent to: as number as int

Table 2. Conversion from Variant using the As Operator
Result of typeof(variant)	Destination Type	Result
"undefined"	boolean	false
"undefined"	number	NaN
"undefined"	int	0
"undefined"	string	"undefined"
"null"	boolean	false
"null"	number	0
"null"	int	0
"null"	string	"null"
"boolean"	any primitive type	equivalent to the result of: boolean as type
"number"	any primitive type	equivalent to the result of: number as type
"string"	any primitive type	equivalent to the result of: string as type
"object"	any primitive type	depends on the actual type of the value
"object"	any object type	reference to the object if the value is an object of the specified type, otherwise null

JSX

Type Conversion