Pipe data from one fn call to another with delivery guarentee

Pipe.js

class Pipe {
    constructor(){
        this.onChangeHandler = null
        this.cache = []
    }
    onChange(fn){
        this.onChangeHandler = fn
        this.flush()
    }
    flush(){
        if(this.cache.length){
            for(const item of this.cache){
                this.onChangeHandler(item)
            }
            this.cache.length = 0
        }
    }
    push(data){
        if(!this.onChangeHandler){
            this.cache.push(data)
        } else {
            this.onChangeHandler(data)
        }
    }
}