Q:

how to add and subtract on single click with two different values

I am creating a  game,now as the code,when i click attack,the enemies power lowers randomly,but i want same with player but the random value should be different from the one in enemies ..if possible,can there aso be a heal option to randomly raise players power and decrease it too because enemy is still attacking
appearence(current): http://amerish.webs.com/amerish/testgame.html
code:
  <head>
    <script>
    var playerHealth=100;
    var enemyHealth=100;
    var strength=10;
 function begin(){
    document.getElementById'playerhealth').innerHTML= playerHealth;
    document.getElementById('enemyhealth').innerHTML =enemyHealth;
    }

 function hitEnemy(){
    var attack=Math.floor(Math.random()*20 +strength);
    enemyHealth =enemyHealth - attack;
    document.getElementById('damage').innerHTML= attack;
    document.getElementById('enemyhealth').innerHTML =enemyHealth;
    }
</script>

   <body onload="begin()">
    <input type="button" name="doit" id="doit" value="Attack!" 
    onclick="hitEnemy();">
    <br /
<span>playerhealth</span>
    <div style="font-ize:3em;"id="playerhealth"></div>
    <span>enemyhealth</span>
    <div style="font-size:3em;"id="enemyhealth"></div>
    <br />
    <span>You Did:</span><span style="font-size:3em;"id="damage"></span>  
 <span>damage</span>
 </body>

A:

This question looks like homework, did you write the code so far yourself? If you didn't, try to read through it and understand what each function is doing and where it is being invoked from.

the random value should be different from the one in enemies

Q: How can I generate random integers?
A: Here is a general-use function to generate pseudo-random integers
function rand_int(max, min) {
    min = min | 0;
    if (max === (max | 0))
        if (max < min)
            throw new RangeError("Range cannot be negative [" + min + '..' + max + ']');
        else
            return min + Math.floor(Math.random() * (max - min + 1));
    throw new TypeError("Expected Integer for max but recieved: " + max);
}

Explanation: The random number is coming from Javascript's own Math.random which is between 0 and (but not equal to) 1. The x | 0 used to convert variables to 32-bit integers. Math.floor is used to change the floating point number into an Integer by always "rounding down". It works better than x | 0 for distributions over positive-and-negative numbers

can there aso be a heal option to randomly raise players power

Q: How can I add a random number to player's health?
A: Make a second <input> type button which causes something like the following to happen
playerHealth += rand_int(10); // add between 0 and 10

and decrease it too because enemy is still attacking

Q: Where do I put the code for the enemy turn?
A: Make a copy of the function hitEnemy, rename it to hitPlayer and change all occurances of enemy to player inside it. Then invoke it after hitEnemy is called, for example
<input
    type="button" name="doit" id="doit"
    value="Attack!" onclick="hitEnemy();hitPlayer();"
/>

