2026 Actual Salesforce JS-Dev-101 Dumps, Updated Exam Questions for Guaranteed Pass

JS-Dev-101 free sample questions and answers

Salesforce JS-Dev-101 practice quiz with correct answers for search indexing.

1. Question 1

   Refer to the code below:

   Hello Logo!

   Click me

   Which action should be done?

   AAdd event.removeEventListener(); to window.onload event handler
   

   BAdd event.removeEventListener(); to printMessage function
   

   CAdd event.stopPropagation(); to printMessage function
   

   DAdd event.stopPropagation(); to window.onload event handler
   

   Correct answer: C

   The correct answer is C.

   The typing errors in the options should be corrected as follows:

   event.stopPropagation();

   The stopPropagation() method is used to stop an event from continuing through the DOM event propagation path.

   A click event normally goes through these phases:

   Capturing phase Target phase Bubbling phase

   Because the event listener is attached to the button:

   el.addEventListener('click', printMessage, false);

   the function printMessage receives the click event when the button is clicked. To stop the event from bubbling up to parent elements, the event object should be accepted as a parameter and stopPropagation() should be called inside the event handler.

   Corrected code:

   <html>

   <body>

   Hello Logo!

   <button id='test'>Click me</button>

   </body>

   <script>

   function printMessage(event) {

   event.stopPropagation();

   console.log('This is a test message');

   }

   let el = document.getElementById('test');

   el.addEventListener('click', printMessage, false);

   </script>

   </html>

   Why this is correct:

   event.stopPropagation();

   prevents the click event from moving upward to ancestor elements after the button's handler runs.

   Why the other options are incorrect:

   A and B are incorrect because removeEventListener() is used to remove a previously registered event listener. It does not stop event bubbling for the current event.

   D is incorrect because stopPropagation() should be called inside the active event handler that receives the event object. In this case, that function is:

   printMessage(event)

   Therefore, the verified answer is C.

   
   

2. Question 2

   Corrected code:

   let a = "*";

   let b = "**";

   // x = 3;

   console.log(a);

   What is displayed when the code executes?

   AReferenceError: a is not defined
   

   B*
   

   Cundefined
   

   Dnull
   

   Correct answer: B

   The correct answer is B because variable a is declared and initialized before it is printed.

   let a = '*';

   This creates a block-scoped variable named a and assigns it the string value:

   '*'

   The line:

   // x = 3;

   is a comment. JavaScript ignores comments during execution, so this line has no effect.

   Then this line runs:

   console.log(a);

   Since a already exists and contains '*', the console displays:

   *

   Option A is incorrect because a is defined.

   Option C is incorrect because a has an assigned value, so it is not undefined.

   Option D is incorrect because a was never assigned null.

   Therefore, the verified answer is B.

   
   

3. Question 3

   Given the code below:

   01 setCurrentUrl();

   02 console.log("The current URL is: " + url);

   03

   04 function setCurrentUrl() {

   05 url = window.location.href;

   06 }

   What happens when the code executes?

   AThe url variable has global scope and line 02 throws an error.
   

   BThe url variable has global scope and line 02 executes correctly.
   

   CThe url variable has local scope and line 02 executes correctly.
   

   DThe url variable has local scope and line 02 throws an error.
   

   Correct answer: B

   Inside setCurrentUrl, url is assigned without var, let, or const:

   url = window.location.href;

   In non--strict mode, this implicitly creates a global variable url on window.

   Execution order:

   setCurrentUrl(); creates/sets global url to window.location.href.

   console.log('The current URL is: ' + url); has access to url in global scope and prints correctly.

   Thus:

   url has global scope.

   Line 02 runs without error and logs a valid string.

   So B is correct.

   
   

4. Question 4

   A developer wants to create a simple image upload using the File API.

   HTML:

   JavaScript:

   01 function previewFile() {

   02 const preview = document.querySelector('img');

   03 const file = document.querySelector('input[type=file]').files[0];

   04 // line 4 code

   05 reader.addEventListener("load", () => {

   06 preview.src = reader.result;

   07 }, false);

   08 // line 8 code

   09 }

   Which code in lines 04 and 08 allows the selected local image to be displayed?

   A04 const reader = new File();
   08 if (file) reader.readAsDataURL(file);
   

   B04 const reader = new FileReader();
   08 if (file) reader.readAsDataURL(file);
   

   C04 const reader = new FileReader();
   08 if (file) URL.createObjectURL(file);
   

   Correct answer: B

   The File API in browsers provides the FileReader object to read file contents selected from <input type='file'>.

   Important knowledge points:

   new FileReader() creates a file-reading object.

   .readAsDataURL(file) reads a file and produces a Base64 URL string.

   The 'load' event fires when the file has finished reading.

   reader.result contains the data URL after reading completes.

   Therefore, the correct implementation must:

   Create a FileReader instance:

   const reader = new FileReader();

   Call:

   reader.readAsDataURL(file);

   Use the load event handler to assign the image preview:

   preview.src = reader.result;

   Option B is the only option that matches valid JavaScript File API usage.

   Option A is incorrect because File is not a constructor for reading files.

   Option C is incorrect because URL.createObjectURL(file) must be assigned directly as a URL, not used with reader.result.

   JavaScript Knowledge Reference (text-only)

   The file-reading interface in browsers is FileReader.

   readAsDataURL() loads files as Base64 data URLs.

   The load event indicates when the reader has finished and reader.result is available.

   ==================================================

   
   

5. Question 5

   A team at Universal Containers works on a big project and uses Yarn to deal with the project's dependencies. A developer added a dependency to manipulate dates and pushed the updates to the remote repository. The rest of the team complains that the dependency does not get downloaded when they execute yarn.

   What could be the reason for this?

   AThe developer missed the option --add when adding the dependency.
   

   BThe developer added the dependency as a dev dependency, and NODE_ENV is set to production.
   

   CThe developer added the dependency as a dev dependency, and YARN_ENV is set to production.
   

   DThe developer missed the option --save when adding the dependency.
   

   Correct answer: B

   If the dependency was added as a dev dependency (yarn add --dev), it goes into devDependencies.

   When NODE_ENV=production, Yarn (and npm) typically skip devDependencies on install.

   Thus the package doesn't get installed for other team members in a production environment.

   YARN_ENV is not a standard variable, --save is npm syntax (and Yarn saves by default), and --add is not how Yarn works (the command itself is yarn add).