For loop in Javascript - Step-by-Step Execution

Concept Flow - For loop

Initialize i=0

↓

Check: i < 5?

No→EXIT

Yes↓

Execute body

↓

Update: i = i+1

↩Back to Check

The for loop starts by setting a variable, checks a condition, runs the code inside if true, then updates the variable and repeats until the condition is false.

Execution Sample

Javascript

for (let i = 0; i < 5; i++) {
  console.log(i);
}

This code prints numbers from 0 to 4, one per line.

Execution Table

Iteration	i value	Condition (i < 5)	Action	Output
1	0	true	Print 0	0
2	1	true	Print 1	1
3	2	true	Print 2	2
4	3	true	Print 3	3
5	4	true	Print 4	4
6	5	false	Exit loop

💡 i reaches 5, condition 5 < 5 is false, loop stops

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	Final
i	0	1	2	3	4	5	5

Key Moments - 3 Insights

Why does the loop stop when i equals 5?

Because the condition i < 5 becomes false at i = 5, so the loop exits as shown in execution_table row 6.

When is the value of i updated during the loop?

i is updated after executing the loop body, before the next condition check, as seen between each iteration in variable_tracker.

Does the loop print the number 5?

No, because the loop stops before printing when i is 5, confirmed by the exit in execution_table row 6.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of i during the 3rd iteration?

A 2

B 3

C 1

D 4

💡 Hint

Check the 'i value' column in the execution_table at iteration 3.

At which iteration does the loop condition become false?

A 5

B 6

C 4

D 1

💡 Hint

Look at the 'Condition (i < 5)' column in execution_table where it changes to false.

If we change the loop to i <= 5, how many times will the loop run?

A 4 times

B 5 times

C 6 times

D 7 times

💡 Hint

Think about the condition i <= 5 allowing i to be 5 inside the loop, check variable_tracker for i values.

Concept Snapshot

for (let i = 0; i < limit; i++) {
  // code to repeat
}
- Initialize i once at start
- Check condition before each loop
- Run code if true
- Update i after each loop
- Stop when condition is false

Full Transcript

A for loop in JavaScript starts by setting a variable i to 0. It then checks if i is less than 5. If yes, it runs the code inside the loop, here printing i. After that, it increases i by 1. This repeats until i is 5, when the condition i < 5 becomes false and the loop stops. The loop prints numbers 0 to 4. The variable i changes from 0 up to 5, but the loop stops before printing 5. This process is shown step-by-step in the execution table and variable tracker.