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Introduction to JavaScript

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Using Comments to Document Code

Sometimes, you may need to prevent a specific part of your code from executing. Deleting the entire code isn't convenient if you want to test a separate section later. There are various scenarios where you may need to temporarily halt the execution of a non-working part of your code. In such cases, comments come to your rescue.

Note

Comments provide a syntax for hiding sections of your code from the interpreter or compiler. They are also valuable for documenting code for other developers.

Single-line Comments

Single-line comments block the entire line of code, ensuring that the code above and below them is executed. The syntax for single-line comments is straightforward: you need to add // before the code on the line you wish to comment out:

console.log("Line 1");
// console.log("Line 2");
console.log("Line 3");

              
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console.log("Line 1");
// console.log("Line 2");
console.log("Line 3");
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The example above shows that the comment // blocks the second code line, which is not executed.

We can also use single-line comments to block multiple lines of code in a row:

console.log("Line 1");
console.log("Line 2");
// console.log("Line 3");
// console.log("Line 4");
console.log("Line 5");

              
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console.log("Line 1");
console.log("Line 2");
// console.log("Line 3");
// console.log("Line 4");
console.log("Line 5");
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Also, we can add the comment at the end of the line.

console.log("Part 1.1"); console.log("Part 1.2");
console.log("Part 2.1"); // console.log("Part 2.2")
console.log("Part 3.1"); console.log("Part 3.2");

              
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console.log("Part 1.1"); console.log("Part 1.2");
console.log("Part 2.1"); // console.log("Part 2.2")
console.log("Part 3.1"); console.log("Part 3.2");
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Multi-line Comments

Consider a situation with a large code block, 299 lines long. Commenting each line individually would be time-consuming. That's where multi-line comments come in handy.

Multi-line comments start with /* and end with */. Any code enclosed within them is commented out:

console.log("Line 1");
console.log("Line 2");
/*
console.log("Line 4");
console.log("Line 5");
console.log("Line 6");
console.log("Line 7");
console.log("Line 8");
console.log("Line 9");
*/
console.log("Line 11");

              
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console.log("Line 1");
console.log("Line 2");
/*
console.log("Line 4");
console.log("Line 5");
console.log("Line 6");
console.log("Line 7");
console.log("Line 8");
console.log("Line 9");
*/
console.log("Line 11");
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In the example above, we can see that code line from 3 to 10 hasn't been executed.

We can use multi-line comments to comment a part of the line:

console.log("Part 1", /* "Part 2", */ "Part 3");

              
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console.log("Part 1", /* "Part 2", */ "Part 3");
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/* console.log("Part 1"); */ console.log("Part 2");

              
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/* console.log("Part 1"); */ console.log("Part 2");
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1. Why are comments used in code?

2. How do we create a single-line comment?

3. What is the syntax for creating a multi-line comment?

4. If you have a large code block and enclose it within /* and */, what happens to the enclosed code?

question mark

Why are comments used in code?

Select the correct answer

question mark

How do we create a single-line comment?

Select the correct answer

question mark

What is the syntax for creating a multi-line comment?

Select the correct answer

question mark

If you have a large code block and enclose it within /* and */, what happens to the enclosed code?

Select the correct answer

Everything was clear?

How can we improve it?

Thanks for your feedback!

Section 1. Chapter 4
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