Date validation with html5 dates
Instead of giving your variables names like dd/mm/yyyy, you should give them names like day, month, year. Other names like d1 or d2. Should have better names.
You need some space between operators. For example, you have this condition in your code: if(dd&lt;10). Stuff like this can be expanded to if(dd &lt; 10). Variable definitions should also not look like this: var x=...;, but rather, var x = ...;.
You should add some more comments, e.g, describe what the functions/code blocks do, and how the processes behind them work.
Finally, just a small nitpicky thing. Both of your functions should be in camelCase. One of them is in underscore_case.