So, JavaScript has a "while" loops and a "do... while" loops. sure, they're written a little bit differently, but ther're mostly the same right?
Wrong!
Here is the syntax for a while loop:

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 var a = 1; //initialize a counter
 while (a < 10) { //sets the loop's condition
 	console.log(a); //code block to execute for each iteration of the loop
 	a++; //increment the counter by 1 for each iteration of the loop
 }
 //outputs 1 2 3 4 5 6 7 8 9
 

And here is the syntax for a do... while loop:

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 var a = 1; //initialize a counter
 do { 
 	//code block to execute for each iteration of the loop
 	console.log(a);
 	a++;  //increment the counter by 1 for each iteration of the loop
 } while (a < 10); //sets the loop's condition
 //outputs 1 2 3 4 5 6 7 8 9
 

The most important difference to note here is that in a "while" loop, the loop's condition is checked before the code block within the curly braces is able to be executed.
So if the condition of a "while" loop is false, the code block won't be executed.

In contrast, in a "do... while" loop, the loop's condition is checked after the first iteration of the code block within the curly braces has already been executed. This is an important distinction, because a "do... while" loop's code block is always executed at least once, regardless of whether it's condition is true or false.

However, a "while" loop's code is only executed if the loop's condition is true.
"while" loops are used far more often than "do... while" loops because you would typically want to check whether a loop's condition is true before you execute the first iteration of it's code block. I also find "while" loops to be easier to read.