The Salesforce Certified JavaScript Developer (JS-Dev-101) exam validates your ability to build and maintain JavaScript applications within the Salesforce ecosystem. This certification is designed for developers who work with Salesforce and need to demonstrate proficiency in modern JavaScript practices, from core language fundamentals to server-side implementations. This page provides a clear roadmap of the exam syllabus, question formats, and practical preparation strategies to help you study efficiently and pass with confidence.
Use this topic map to guide your study for Salesforce JS-Dev-101 (Salesforce Certified JavaScript Developer) within the Salesforce Developer path.
The JS-Dev-101 exam uses a mix of question types to assess both theoretical knowledge and practical problem-solving ability. Questions progress in difficulty and reflect real-world scenarios you will encounter as a Salesforce Developer.
An effective study plan breaks the syllabus into manageable weekly blocks, combines concept review with hands-on practice, and includes timed mock exams to build confidence and pacing. Dedicate time to each topic area proportionally, with extra focus on asynchronous programming and server-side JavaScript, which often appear heavily on the exam.
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Asynchronous Programming and Server Side JavaScript typically account for a significant portion of the exam, as these are critical skills in real Salesforce projects. Objects, Functions, and Classes also appear frequently because they form the foundation for building maintainable, scalable applications. Allocate study time proportionally to these areas while ensuring you have solid coverage across all seven topic domains.
Variables, Types, and Collections provide the data structures you use throughout your code. Objects and Functions let you organize that data and logic into reusable modules. Browser and Events handle user interactions that trigger your functions. Asynchronous Programming manages long-running operations like API calls without freezing the UI. Server Side JavaScript extends your capabilities to backend services. Testing validates that all these pieces work together correctly in production. Understanding these connections helps you see the exam as a cohesive whole rather than isolated topics.
Ideally, you should have completed at least one or two small projects using JavaScript in a Salesforce context, such as building a Lightning Web Component or a Node.js script that calls Salesforce APIs. Hands-on experience helps you recognize patterns and understand why certain approaches work better than others. If you are new to JavaScript, prioritize coding labs and practice exercises that let you write, run, and debug code before attempting the exam.
Misunderstanding asynchronous execution order and promise chains is a frequent source of lost points. Candidates often confuse variable scope and closure behavior, especially in nested functions and callbacks. Another common error is overlooking error handling best practices or failing to recognize when try-catch blocks are necessary. Review these three areas carefully in your final week, and use the practice test to identify your personal weak spots.
In your final week, shift from learning new material to reinforcing what you have studied. Take a full-length timed practice test to identify any remaining gaps and build exam pacing. Review the explanations for every question you miss, not just the ones you guessed on. Do short, focused review sessions on your weakest topics rather than trying to re-study everything. Get adequate sleep the night before the exam, and avoid cramming new concepts on exam day.
A developer initiates a server with the file server.js and adds dependencies in the source code's package.json that are required to run the server.
Which command should the developer run to start the server locally?
Comprehensive and Detailed Explanation From JavaScript/Node.js Knowledge:
In a Node.js project that uses package.json, you typically define a 'start' script:
{
'scripts': {
'start': 'node server.js'
}
}
Then you start the app with:
npm start
npm start:
Looks up the 'start' script in package.json.
Runs the command defined there (commonly node server.js).
This is the standard way to start a Node.js app with npm-managed dependencies.
Why others are incorrect:
A . node start
Tries to run a file named start with Node; does not use package.json scripts.
C . npm start server.js
npm start does not take the script filename as an argument in this way; it just runs the start script as defined.
D . start server.js
Not an npm or node command; on some shells it just tries to ''start'' a process but is not the standard Node/npm workflow.
Relevant concepts: package.json, npm scripts, npm start, Node entry file execution.
A developer writes the code below to return a message to a user attempting to register a new username. If the username is available, a variable named msg is declared and assigned a value on line 03.
function getAvailabilityMessage(item) {
if (getAvailability(item)) {
var msg = "Username available";
return msg;
}
}
The correct answer is C.
When getAvailability(item) returns true, the code inside the if block executes:
var msg = 'Username available';
return msg;
The variable msg receives the string value:
'Username available'
Then that same value is returned from the function.
The key point is that var is function-scoped, not block-scoped. So msg belongs to the function scope of getAvailabilityMessage(). However, because the return msg; statement is inside the same if block, the function immediately returns the assigned string when the username is available.
Option A is incorrect because msg is defined before it is returned.
Option B is incorrect because 'newUserName' is not assigned or returned anywhere in the function.
Option D would only happen if getAvailability(item) returned false, because then the function would finish without an explicit return value.
For the available username scenario, the verified answer is C.
Refer to the code below:
01 let total = 10;
02 const interval = setInterval(() => {
03 total++;
04 clearInterval(interval);
05 total++;
06 }, 0);
07 total++;
08 console.log(total);
Considering that JavaScript is single-threaded, what is the output of line 08 after the code executes?
Synchronous execution order
JavaScript executes code in a single thread, following a well-defined order:
All synchronous code runs first, line by line.
Asynchronous callbacks (like those scheduled with setInterval or setTimeout) are placed into the event queue and executed only after the current call stack is empty.
Let's follow the code step by step:
Line 01:
let total = 10;
total is initialized with the value 10.
Line 02:
const interval = setInterval(() => {
total++;
clearInterval(interval);
total++;
}, 0);
setInterval schedules the callback function to run repeatedly after a delay of at least 0 milliseconds, but it does not run immediately. The callback is added to the timer queue and will be invoked after the current synchronous script finishes and the event loop gets to process timer callbacks.
At this point, interval holds the interval ID, but the callback has not executed yet.
Line 07:
total++;
This is still synchronous, so it runs before any scheduled callbacks.
total was 10, now it becomes 11.
Line 08:
console.log(total);
At this moment, the interval callback has still not run (because the event loop has not yet processed the timer queue).
So total is 11, and console.log(total); outputs 11.
Therefore, the value printed at line 08 is 11, making option A correct.
What happens after the log (for understanding, not affecting the answer)
After the main script finishes, the event loop processes the timer callback for setInterval:
Callback:
() => {
total++; // from 11 to 12
clearInterval(interval); // cancels further executions
total++; // from 12 to 13
}
So eventually total becomes 13, but this happens after console.log(total) has already executed. Since the question asks specifically for the output at line 08, the asynchronous updates do not change that line's output.
Why other options are incorrect
Option B (12): This would require the callback to run before the log, which does not happen because asynchronous callbacks are queued and executed after the current stack finishes.
Option C (10): Ignores the total++ on line 07.
Option D (13): This is the final value after the callback finishes, but it occurs after the console.log line executes, not at the time line 08 runs.
JavaScript knowledge references (descriptive, no links):
JavaScript is single-threaded and uses an event loop with a call stack and task queues.
setInterval schedules callbacks to run asynchronously after a minimum delay; the callback never runs before the current synchronous code finishes.
Synchronous statements like total++ on line 07 execute before any queued interval callback.
A developer is leading the creation of a new web server for their team that will fulfill API requests from an existing client. The team wants a web server that runs on Node.js, and they want to use the new web framework Minimalist.js. The lead developer wants to advocate for a more seasoned back-end framework that already has a community around it.
Which two frameworks could the lead developer advocate for?
The question is about:
Web frameworks that run on Node.js
Used to build servers and APIs
With established communities.
From the given options:
Angular:
A front-end framework running in the browser, not a Node.js server framework.
Gatsby:
A React-based static site generator; uses Node tooling but is not primarily a Node server framework.
Next / Next.js:
Server-side rendering / full-stack frameworks built on Node.js and React.
Used to create both server-rendered pages and APIs.
They have active communities and are ''seasoned'' compared to a hypothetical Minimalist.js.
Although typical Node back-end frameworks would include Express.js, Koa, or NestJS, given the options provided, the best fits for server-side frameworks with Node.js and an ecosystem are:
Next (interpreted as Next.js)
Next.js
Thus, the correct pair from the list is B and D.
Concepts: Node.js web frameworks, server-side rendering, community-backed frameworks vs minimal/new frameworks.
let sampleText = "The quick brown fox jumps";
Which three expressions return true for a substring?
The correct answers are A, B, and C.
The original variable name appears to contain a typing error. The variable should be used consistently as sampleText:
let sampleText = 'The quick brown fox jumps';
A is correct because includes() checks whether a string contains a specific substring and returns a Boolean value:
sampleText.includes('fox');
Since 'fox' exists inside 'The quick brown fox jumps', this returns:
true
B is correct after correcting the typing error. The correct expression is:
sampleText.indexOf('quick') > -1;
indexOf() returns the index position where the substring is found. If the substring is not found, it returns -1.
Since 'quick' exists in the string, sampleText.indexOf('quick') returns a value greater than -1, so the expression returns:
true
C is correct after correcting the missing quotation marks and adding a Boolean comparison:
sampleText.indexOf('fox') !== -1;
The substring 'fox' exists in the string, so indexOf('fox') does not return -1. Therefore, the expression returns:
true
D is incorrect because the method name is typed incorrectly. JavaScript string has includes(), not include().
Incorrect:
sampleText.include('fox')
Correct:
sampleText.includes('fox')
E is incorrect because JavaScript string matching is case-sensitive:
sampleText.indexOf('Quick') !== -1;
The string contains 'quick' with a lowercase q, not 'Quick' with an uppercase Q, so this returns:
false
Therefore, the verified answers are A, B, and C.
