You have an infinite loop, because if numbers[i] > 70 it's not increasing i, so the next loop it's checking that same condition again without an incremented i value. There are multiple ways to fix this, but one option is to output the value when numbers[i] <= 70, and always increment i.

var numbers = [12, 34, 23, 98, 08, 78, 73, 48];
var i = 0;

while (i < numbers.length){
    if (numbers[i] <= 70){
        console.log(numbers[i]);
    }
    
    i++;
}

Another option would be a different loop:

var numbers = [12, 34, 23, 98, 08, 78, 73, 48];
var i = 0;

for(i = 0; i < numbers.length; i++) {
    if (numbers[i] > 70){
       continue;
    }
    
    console.log(numbers[i]);
}

Or a simpler way:

var numbers = [12, 34, 23, 98, 08, 78, 73, 48];
var i = 0;

for(i = 0; i < numbers.length; i++) {
    if (numbers[i] <= 70){
        console.log(numbers[i]);
    }
}

Check out this jsFiddle: http://jsfiddle.net/YdpJ2/3/

var getFalse = function() {
  alert("Called getFalse!");
  return false;
};

do {
  continue;
  alert("Past the continue? That's impossible.");
} while( getFalse() );​

It appears to hit the continue, then break out of that iteration to run the check condition. Since the condition is false, it terminates.