Method push

stacks/queue-via-stacks.js:11–14

(x)

  }

  push(x) {
    /* Push into stackNewest; wich always has the newes elements on top */
    this.stackNewest.push(x);
  }

  /* muve elements from stackNewest into stackOldest. This is usually done so that 
     we can do operations on stackOldest. */