To inline JavaScript code in the middle of genericjs section code, use the __asm__ keyword. Similar to a traditional architecture, the __asm__ keyword lets you to write native (JavaScript) code. This functionality can be used to interface with external JS libraries which have no Cheerp-compatible headers yet.

__asm__(code : output constraints : input constraints : clobber constraints)
  • __asm__ is only supported in functions tagged with the [[genericjs]] attribute.
  • Code inside __asm__ should never throw to the external scope, and should consist of a single JS expression or statement without the final ;.
  • Both the input constraints and clobber constraints parts are optional.
  • Only the "r" constraint is supported. It represents a local variable in the generated JS code (equivalent to a register on traditional architecture).
  • Only integral types, floating point types and pointers to object in the client namespace (i.e. DOM or native JavaScript objects) can be used.


__asm__("alert('Alert from __asm__')");

It is possible to pass arguments and get values back from inline JavaScript:

int stringLength;
client::String* stringFromDom = ...;
__asm__("%1.length" : "=r"(stringLength) : "r"(stringFromDom));
assert(stringLength == stringFromDom->get_length());
Was this page helpful?
Suggest changes