Obsolete since JSAPI 32
This feature is obsolete. Although it may still work in some browsers, its use is discouraged since it could be removed at any time. Try to avoid using it.
jsdouble JSVAL_TO_DOUBLE(jsval v);
JSVAL_TO_DOUBLE casts a specified JS value,
v, to a C floating-point number of type
jsdouble. As a precondition,
must be true. This function is not type-safe: if
v is an integer, string, null, or anything else, the behavior is undefined.
To convert any value to a number, use