Create a card matching game to test the player's memory.

This mockup shows a game in progress: the player has matched four cards, and just revealed two non-matching cards.

This mockup shows a completed game, where the player can click the button to start again.

Requirements

• Cards should be laid out on a 6x6 grid, all face down initially (i.e. numbers not showing)
• There should be a total of 36 cards with the numbers 1-18 (two of each), placed randomly on the grid
• Clicking a card should 'reveal' it - showing the hidden number of the card
• Clicking a second card should reveal that card
• If the second card has the same number as the first card, both cards should be removed from the board after 3 seconds
• If the second card has a different number to the first card, both cards should be 'hidden' again after 3 seconds (i.e. turned face down)
• The user shouldn't be able to turn over any more cards until the 3 second timer completes and the two revealed cards are either removed (if they matched), or hidden again (if they didn't)
• Once all cards are removed from the board, the game is over and the 'Play again' button should be shown
• Clicking 'Play again' should generate a new, random set of cards on the grid