Comments
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Expert Answer & Key Takeaways
Mastering Comments is essential for high-fidelity technical architecture and senior engineering roles in 2026.
JavaScript Comments
JavaScript comments are used to explain JavaScript code, and to make it more readable. They can also be used to prevent execution when testing alternative code.
1. Single Line Comments
Single line comments start with
//. Any text between // and the end of the line will be ignored by JavaScript (will not be executed).// Change heading:
document.getElementById("myH").innerHTML = "My First Page";
// Change paragraph:
document.getElementById("myP").innerHTML = "My first paragraph.";2. Multi-line Comments
Multi-line comments start with
/* and end with */. Any text between /* and */ will be ignored by JavaScript./*
The code below will change
the heading with id = "myH"
and the paragraph with id = "myP"
in my web page:
*/
document.getElementById("myH").innerHTML = "My First Page";
document.getElementById("myP").innerHTML = "My first paragraph.";It is most common to use single line comments. Block comments are often used for formal documentation.
3. Using Comments to Prevent Execution
Using comments to prevent execution of code is suitable for code testing. Adding
// in front of a code line changes the code lines from an executable line to a comment.// document.getElementById("myH").innerHTML = "My First Page";
document.getElementById("myP").innerHTML = "My first paragraph.";This example uses a code block to prevent execution of multiple lines:
/*
document.getElementById("myH").innerHTML = "My First Page";
document.getElementById("myP").innerHTML = "My first paragraph.";
*/Top Interview Questions
?Interview Question
Q:When should you use multi-line comments instead of single-line?
A:
Multi-line comments are best for formal documentation or for commenting out large blocks of code during testing. For quick explanations on a single line, single-line (//) comments are preferred as they are cleaner.
?Interview Question
Q:Do comments affect the performance of a website?
A:
No, comments are stripped out by modern minifiers during the build process and ignored by the JavaScript engine at runtime, so they have zero impact on performance.
?Interview Question
Q:What character sequence starts a multi-line comment?
A:
A multi-line comment starts with /* and ends with */.
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