Course Content
Introduction to JavaScript
Introduction to JavaScript
for
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:
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:
for (let i = 1; i < 5; i++) { console.log("Loop iteration:", i); };
In this example:
let i = 1
: Initialization, where we create the variablei
inside thefor
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 thefor
loop.
Each step in the loop can be described as follows:
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:
for (let i = 15; i > 10; i--) { console.log("i =", i); }
The for
loop counter is unique to its scope, so you don't need to worry about the counter name conflicting with other variables:
let i = 2077; console.log("(global) i =", i); for (let i = 0; i < 4; i++) { console.log("(for) i =", i); } console.log("(global) i =", i);
Different expressions for Increment/Decrement operations can be used as well:
for (let i = 0; i < 40; i += 7) { console.log("i =", i); };
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:
// `while` let a = 1; while (a <= 3) { console.log("While:", a); a++; } // `for` for (let i = 1; i <= 3; i++) { console.log("For:", i); }
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.
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