Why do ARM chips have an instruction with JavaScript in the name (FJCVTZS)?

Cool. Looks like V8 can use it: https://chromium.googlesource.com/v8/v8/+/93f85699e22df95861...

See also FCVTMOD.W.D in RISC-V. The fact that you have to provide a way covert doubles to int32 like x86 does because of JavaScript is a weird design greeble all future ISAs will probably have til the end of time…