A nested loop in JavaScript is a loop that is inside another loop. The inner loop will execute its code block for each iteration of the outer loop. Here is an example:
for (let i = 1; i <= 3; i++) {
console.log("Outer Loop: " + i);
for (let j = 1; j <= 2; j++) {
console.log("Inner Loop: " + j);
}
}
In this example, the outer loop will iterate 3 times, and for each iteration of the outer loop, the inner loop will iterate 2 times. So the output will be:
Outer Loop: 1
Inner Loop: 1
Inner Loop: 2
Outer Loop: 2
Inner Loop: 1
Inner Loop: 2
Outer Loop: 3
Inner Loop: 1
Inner Loop: 2
Note that, the inner loop will execute its code block for each iteration of the outer loop and the inner loop will execute its code block for each iteration of the outer loop.