verem

let ml = {
    push( k ) {
        this.begin = { key: k, next: this.begin }
    },
    pop() {
        if (this.begin) {
            let rv = this.begin
            this.begin = this.begin.next
            return rv.key
        }
    },
    forEach( f ) {
        let e = this.begin, i = 0
        while (e) {
            f( e.key, i++, e )
            e = e.next
        }
    }
}

ml.push(6)
ml.push(4)
ml.push(3)
ml.push(7)

ml.pop()

ml.forEach( v => console.log(v) )

console.log(
    JSON.stringify(ml)
)