IterableWeakMap.js

// This is implementing a iterable WeakMap
// It has the same methods as WeakMap and in addition:
// It's keys and values are readable properties.
// It can be iterated by map and reduce, Arguments: key, value
class IterableWeakMap{
    constructor(){
        Object.defineProperties(this,{
            keys:{
                enumerable: false,
                writable: true,
                value: []
            },
            values:{
                enumerable: false,
                writable: true,
                value: []
            },
            __Mapping__:{
                enumerable: false,
                writable: false,
                value: new WeakMap()
            },
            length:{
                enumerable: false,
                writable: true,
                value: 0
            }
        });
    }
    set(key,value){
        const index=this.__Mapping__.get(key);
        if(index===undefined){
            let newIndex;
            // write
            newIndex=this.keys.push(key)-1;
            this.values.push(value);
            this.__Mapping__.set(key,newIndex);
            this.length++; 
        }else{
            // overwrite
            this.values[index]=value;
        }
    }
    get(key){
        const index=this.__Mapping__.get(key);
        if(index!==undefined){
            return this.values[index];
        }
    }
    has(key){
        const index=this.__Mapping__.get(key);
        return index!==undefined;
    }
    map(func){
        return this.keys.map((value,index)=>func(this.values[index],value));
    }
    filter(func){
        return this.keys.filter((value,index)=>{
            return func(this.values[index],value);
        });
    }
    delete(key){
        const index=this.__Mapping__.get(key);
        const iExists=index!==undefined;
        if(iExists){
            delete this.keys[index];
            delete this.values[index];
            this.__Mapping__.delete(key);
            this.length--;
        }
        return iExists;
    }
}