In JavaScript, an expression is any valid block of code that results in a value. For example,
console.log(1 === 1)
would produce the boolean value true.
Loops are used in JavaScript are used to perform an action repeatedly. An example of this would be the following:
for(let i = 1; i <= 10; i++ ){
console.log(5 * i);
}
This block of code would log the first 10 numbers of the 5 times table, ending at 5 x 10 as i would be equal to 10 and the condition for the loop to end would be met.
Another common form of loop in JavaScript is the while loop which executes until a condition defined when the statement is created is met, for example:
let i = 1;
while(i <= 10){
console.log(5 * i);
i++;
}