Take a look at commonly used in oop inheritance pattern for extending base
class:
class Animal {
constructor(){
this.done = 0
}
doIt(){
this.done++
}
}
class Cat extends Animal {}
class Dog extends Animal {}
class Dog1 extends Animal {}
class Dog2 extends Animal {}
class Dog3 extends Animal {}
function testAnimal(animal){
for(var i = 0; i < 100000; i++){
animal.doIt();
}
}
function test(){
var cat = new Cat();
testAnimal(cat)
var dog = new Dog();
testAnimal(dog)
var dog1 = new Dog1();
testAnimal(dog1)
var dog2 = new Dog2();
testAnimal(dog2)
var dog3 = new Dog3();
testAnimal(dog3)
}
test()
Running in latest node (6.0.287.53 v8 version) I get the following results:
Invoking testAnimal function with first descendant class Cat, V8 does a
great job by compiling to doIt() method and "this.done++" incrementation to
REX.W asm instruction without any calls to slow-runtime c++ function for
generic field access.Than, by invoking doIt() on second descendant class
Dog, V8 fall down to doIt() method deoptimization (and all outer functions
which also were inlined) and add few ams rew.x and one jz instruction to
check hidden map for second Dog class. Than on invoking doIt() on each new
subclass v8 again fall down to deoptimization and add new checks for new
hidden map and finally on fourth descendant class Dog3 v8 give up and for
"this.done++" goes to call LoadICTrampoline StoreICStrictTrampoline c++
runtime function for generic access. I hope its only bug and v8 can
efficient deal with inheritance and accessing field without slow runtime
generic filed access otherwise the big question came in - is "extend"
keyword a performance antipattern and why v8 can't implement something like
c++ v-table mechanism ?
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