The if...else statement executes one set of statements if a specified condition is true, and another if it is false.
NOTE:
You shouldn't use simple assignment statements such as if(a = b) in a conditional statement. To compare two variables, remember to use the == operator.
if(calcaverage(x,y,z) < 10)
document.write("The average is less than 10.");
else
document.write("The average is 10 or more.");
This example tests the result of a function and displays one of two messages depending on whether the result is less than 10 or not: