gistfile1.txt

#!/usr/local/bin/node

//NOW WITH NODE.JS

n=2000000;
sumPrimes=0;
myPrimes = new Array();

// set all array values to true

for (i=2;i<=n;i++)
	{
	myPrimes[i]=true;
	}

// sieve of eratosthenes

for (i=2;i<=n/2;i++)
	{
	if (myPrimes[i])
		{
		for (j=2*i;j<=n;j+=i)
			{
			myPrimes[j]=false;
			}
		}	
	}
	
// add up unsieved primes	
	
for (i=2;i<=n;i++)
	{
	if(myPrimes[i])
		{
		sumPrimes+=i;
		}
	}
	
console.log(sumPrimes);	

You can do this with just your middle loop.

First of all, you don't need to initialize your array. I applaud, it's the good thing to do, but it's not necessary. Before you touch values in the array, myPrimes[anything] is false.

Your sieve implementation was basically exactly like mine.

The n/2 trick is good. I didn't do that.

You don't need a separate loop to add up the primes, you can just accrue the sum as you go along.

#!/usr/local/bin/node

max = 2000000;
var sum = 0;
var prime = new Array();

for (iter = 2; iter < max; iter++) {
    if (!prime[iter]) {
        sum += iter;
        for (i = iter*2; i < max; i += iter) {
            prime[i]=1;
        }
    }
}

console.log("The sum is", sum);

Yes- it is smart to use just one loop!