User Guide

358 Chapter 21: C-Level Extensibility
JSBool JS_ValueToDouble()
Description
This function extracts a function argument from a jsval structure, converts it to a double (if
possible), and passes the converted value back to the caller.
Arguments
JSContext *cx
, jsval v, double *dp
• The cx argument is the opaque JSContext pointer that passed to the JavaScript function.
• The v argument is the jsval structure from which the double is to be extracted.
• The dp argument is a pointer to an 8-byte double. This function stores the converted value
in
*dp.
Returns
A Boolean value: JS_TRUE indicates success; JS_FALSE indicates failure.
JSBool JS_ValueToBoolean()
Description
This function extracts a function argument from a jsval structure, converts it to a Boolean value
(if possible), and passes the converted value back to the caller.
Arguments
JSContext *cx
, jsval v, JSBool *bp
• The cx argument is the opaque JSContext pointer that passes to the JavaScript function.
• The v argument is the jsval structure from which the Boolean value is to be extracted.
• The bp argument is a pointer to a JSBool Boolean value. This function stores the converted
value in
*bp.
Returns
A Boolean value: JS_TRUE indicates success; JS_FALSE indicates failure.
JSBool JS_ValueToObject()
Description
This function extracts a function argument from a jsval structure, converts it to an object (if
possible), and passes the converted value back to the caller. If the object is an array, use
JS_GetArrayLength() and JS_GetElement() to read its contents.
Arguments
JSContext *cx, jsval v, JSObject **op
• The cx argument is the opaque JSContext pointer that passes to the JavaScript function.
• The v argument is the jsval structure from which the object is to be extracted.
• The op argument is a pointer to a JSObject pointer. This function stores the converted value
in
*op.