The for loop is a fundamental looping structure in JavaScript, though it can initially be challenging to understand. It uses the for keyword and requires three parameters enclosed in parentheses:

for (Initialization; Condition; Increment / Decrement) {
  // code block
}

Here's a breakdown of these parameters:

• Initialization: This is where you initialize a new counter used by the for loop. It's executed only once;
• Condition: An expression checked before each iteration, similar to the while loop;
• Increment/Decrement: Operations performed on the counter at the end of each loop iteration.

Note

Iteration in loops refers to repeating a block of code a certain number of times or until a specific condition is met. Each time the block of code is executed, it's considered one iteration.

Let's illustrate this with an example:

In this example:

• let i = 1: Initialization, where we create the variable i inside the for loop. This operation executes once;
• i < 5: Condition, checked before each iteration;
• i++: Increment expression, executed after each iteration;
• console.log("Loop iteration:", i);: Body of the for loop.

Each step in the loop can be described as follows:

// Step 1: Counter initialization
let i = 1;
// Step 2: Main loop body
if (i < 5) { // Condition check
  console.log("Loop iteration:", i); // Loop body
}
i++; // Increment operation

Step 2 repeats until the condition becomes false.

It can be beneficial to consider a diagram to gain a clearer understanding of how the loop operates.

You can also use decrement in the for loop, as shown here:

The for loop counter is unique to its scope, so you don't need to worry about the counter name conflicting with other variables:

Different expressions for Increment/Decrement operations can be used as well:

Comparing the for and while loops

When comparing for and while loops, the for loop is often simpler and more concise. Here's an example of equivalent loops:

In this comparison, the for loop is more straightforward and occupies less code space. Additionally, the for loop automatically clears the counter variable (in this case, i) after execution.