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JavaScript comments can be used to explain JavaScript code, and to make it more readable. JavaScript comments can also be used to prevent execution, when testing alternative code.
//.
// and the end of the line will be ignored by JavaScript (will not be executed).
Formula
This example uses a single - line comment before each code line:// Change heading:
document.getElementById("myH").innerHTML = "My First Page";// Change paragraph:
document.getElementById("myP").innerHTML = "My first paragraph.";This example uses a single line comment at the end of each line to explain the code:
let x = 5; // Declare x, give it the value of 5 let y = x + 2; // Declare y, give it the value of x + 2/* and end with */.
/* and */ will be ignored by JavaScript.
Formula
This example uses a multi - line comment (a comment block) to explain the code:/* 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.
Using comments to prevent execution of code is suitable for code testing.
// in front of a code line changes the code lines from an executable line to a comment. This example uses // to prevent execution of one of the code lines:
//document.getElementById("myH").innerHTML = "My First Page";
document.getElementById("myP").innerHTML = "My first paragraph.";This example uses a comment block to prevent execution of multiple lines:
/*
document.getElementById("myH").innerHTML = "My First Page";
document.getElementById("myP").innerHTML = "My first paragraph.";*/