For Loop

JavaScript For loops are a little bit complicated, but you really need to understand them. It is a combination of a statement, a condition, and another statement. Typically, for loops iterate through code multiple times known as a loop. The great thing about for loops is that you can program them to run exactly how many times you want. Let’s just go ahead and jump into an example.

for(var i = 0; i < 5; i++) //statement 1 var i = 0; condition i<5; statement2 i++;
{
    document.write(i);
    //write current value of variable i
    document.write('&lt;br/&gt;');
}
document.write(" End of for loop ");  

The for loop is somewhat like a modified if statement that restarts itself until the condition is satisfied. Inside of the for loop we have a statement var i = 0; that declares a variable i and sets it equal to 0. Next, we have the conditional i < 5 that is the if part of the statement. We know that the conditional says if i < 5, then run the statements in the { }. Finally, we have an increment operator statement, i++, which is the most commonly used way to advance a for loop.

Since the ++ is after the variable, we will increment i after all of the statements in the { } have been executed. This is exactly why when we print i, document.write(i), for the first time it is 0 rather than 1. So, we run through the statements in the { } and we get the results 0,1,2,3,4. Right after the final execution of statements, i is incremented to 5, which was then compared against the conditional i < 5. It obviously is false at this stage; therefore, we move outside of the for loop and we execute the next line of code that happens to be our document.write(” End of for loop “); statement.

References

• js For Loop (w3schools)
• Best way to write a for loop (impressivewebs)
• JavaScript For Loop (tizag)