JavaScript | Comments
Comments are used to prevent the execution of statements. Comments are ignored while the compiler executes the code. Comments are user-friendly as users can get explanations of code using comments.
Syntax:
// For single line comment
/* For block of lines comment ... ... */
Return Value: During execution of code, comments are ignored.
Example 1: This example illustrates the single line comment using //.
html
<!DOCTYPE html> < html > < head > < title > JavaScript Comments </ title > < script > // Function to add two numbers function add() { // Declare three variables var x, y, z; // Input a number and store it into variable x x = Number( document.getElementById("num1").value ); // Input a number and store it into variable x y = Number( document.getElementById("num2").value ); // Sum of two numbers z= x +y; // Return the sum document.getElementById("sum").value = z; } </ script > </ head > < body > Enter the First number: < input id = "num1" >< br >< br > Enter the Second number: < input id = "num2" >< br >< br > < button onclick = "add()" > Sum </ button > < input id = "sum" > </ body > </ html > |
Output:
Before clicking on the button:

After clicking on the button:

Example 2: This example illustrates the multi-line comment using /* … */
html
<!DOCTYPE html> < html > < head > < title > JavaScript Comments </ title > < script > /* Script to get two input from user and add them */ function add() { /* Declare three variable */ var x, y, z; /* Input the two nos. num1, num2 Input num1 and store it in x Input num2 and store it in y The sum is stored in a variable z*/ x = Number(document.getElementById("num1").value); y = Number(document.getElementById("num2").value); z = x + y; document.getElementById("sum").value = z; } </ script > </ head > < body > Enter the First number : < input id = "num1" >< br >< br > Enter the Second number: < input id = "num2" >< br >< br > < button onclick = "add()" > Sum </ button > < input id = "sum" > </ body > </ html > |
Output:
Before clicking on the button:

After clicking on the button:

Example 3: This example illustrates that commented code will never execute.
html
<!DOCTYPE html> < html > < head > < title > JavaScript Comments </ title > < script > function add() { var x, y, z; x = Number( document.getElementById("num1").value ); y = Number( document.getElementById("num2").value ); z= x +y; // Comment the code section //document.getElementById("sum").value = z; } </ script > </ head > < body > Enter the First number: < input id = "num1" >< br >< br > Enter the Second number: < input id = "num2" >< br >< br > < button onclick = "add()" > Sum </ button > < input id = "sum" > </ body > </ html > |
Output:
Before clicking on the button:

After clicking on the button:
