Updated for Latest JavaScript Developer I Exam
Last Updated: November 2025 | Based on current Salesforce JavaScript Developer I exam guide
This guide covers the Salesforce JavaScript Developer I exam: format, domains, objectives, and realistic practice questions. The focus is on core JavaScript (variables, collections, functions, classes, async, testing) plus applying JS in the browser and server-side.
💡 What is Salesforce JavaScript Developer I?
Validates your ability to use modern JavaScript to build front-end and back-end web apps, including concepts like variables, collections, objects, functions, classes, async, testing, and debugging.
Intended for developers with 1+ year of experience building apps with JavaScript (browser or Node.js), including those working with Lightning Web Components (LWC).
Pairs perfectly with Platform Developer I. JS Dev I shows your strength in language & web stack, while PD I covers Apex and Salesforce platform development.
Salesforce Certified JavaScript Developer I
Exam guide for developers who use JavaScript to build web apps, including Lightning Web Components.
Expect questions around core language features, browser & events, async, Node.js, testing, and debugging.
📊 JavaScript Developer I Exam at a Glance
📝 Note: These details (questions, duration, passing score, fees) are based on the current Salesforce exam guide and trusted community resources. Always confirm on the official exam page before scheduling.
👤 Who Should Take the JavaScript Developer I Exam?
- Front-end, back-end, or full-stack web developers using JavaScript daily.
- Salesforce developers working with Lightning Web Components (LWC) or web integrations.
- Engineers who want a credential that proves clean, modern JS skills, independent of a specific framework.
- PD I-certified developers who want to strengthen their language fundamentals and web stack knowledge.
Exam Objectives & Weightage (JavaScript Developer I)
1. Variables, Types, and Collections
23%Core language fundamentals: variables, primitives, arrays, JSON, truthy/falsy, type coercion. :contentReference[oaicite:1]{index=1}
- Create and initialize variables correctly with
let,const, andvar. - Work with strings, numbers, dates, and understand type coercion.
- Recognize truthy/falsy values in conditionals.
- Manipulate arrays: map, filter, reduce, sorting, and iteration.
- Use and manipulate JSON for API responses and data structures.
2. Objects, Functions, and Classes
25%How you structure and reuse your JavaScript: objects, functions, modules, and classes. :contentReference[oaicite:2]{index=2}
- Use object literals, property access, and nested structures.
- Choose the right kind of function (declaration, expression, arrow) and understand scope and this.
- Design and use ES6 classes, constructors, inheritance, and static members.
- Work with modules (
import/export) and reusable utilities. - Follow best practices for clean, maintainable JavaScript.
3. Browser and Events
17%Interacting with the browser: DOM, events, dev tools, browser APIs. :contentReference[oaicite:3]{index=3}
- Register and handle events, understand bubbling and capturing.
- Manipulate the DOM (query selectors, create/update/remove nodes).
- Use browser dev tools to inspect elements, network calls, and console logs.
- Work with common browser APIs (storage, timers, etc.).
4. Debugging and Error Handling
7%Find and fix bugs effectively using console, breakpoints, and try/catch. :contentReference[oaicite:4]{index=4}
- Use console and browser dev tools to inspect variables and flow.
- Handle errors with try/catch/finally, custom error objects.
- Understand common JS error types and how to resolve them.
5. Asynchronous Programming
13%Work with callbacks, promises, async/await, and the event loop. :contentReference[oaicite:5]{index=5}
- Convert callback-based code to promises or async/await.
- Understand the event loop and microtasks vs macrotasks.
- Handle async errors correctly and avoid “callback hell”.
6. Server-Side JavaScript
8%Basics of using JavaScript on the server (often with Node.js). :contentReference[oaicite:6]{index=6}
- Understand Node.js and when to use it.
- Know common Node.js modules and package management (npm, yarn).
- Recognize scenarios where server-side JS is a good fit.
7. Testing
7%Writing and evaluating unit tests for JavaScript code. :contentReference[oaicite:7]{index=7}
- Understand test structure (arrange–act–assert).
- Identify ineffective tests and improve them.
- Test async code and error conditions.
📝 Sample JavaScript Developer I Questions
💡 Scenario-Driven & Code-Focused
Many questions show code snippets and ask what they output or which option is the best fix. Practice reading code carefully and reasoning through execution.
Question 1: Variables & Types
let x = '5'; let y = 2; console.log(x + y);
What is logged to the console?
A) 7
B) '7'
C) '52'
D) It throws a TypeError.
✓ Correct Answer: C) '52'
Explanation: The + operator with a string operand causes string concatenation.
'5' + 2 coerces 2 to '2', producing '52'.
Question 2: Objects & Functions
const user = {
name: 'Ana',
greet() {
console.log(`Hi, I'm ${this.name}`);
}
};
const greet = user.greet;
greet();
What happens when greet() is called?
A) Logs Hi, I'm Ana
B) Logs Hi, I'm undefined
C) Throws a TypeError because this is null
D) Throws a ReferenceError because name is not defined
✓ Correct Answer: B) Logs Hi, I'm undefined
Explanation: When user.greet is stored in greet and called standalone, this
is no longer bound to user. In non-strict mode it points to window/global, which has no name property,
so this.name is undefined.
Question 3: Browser & Events
What is logged when the button is clicked?
A) true
B) false
C) undefined
D) It throws an error.
✓ Correct Answer: B) false
Explanation: Arrow functions don’t bind their own this; they capture this from the surrounding scope
(likely window). this is not the button, so this === btn is false.
Question 4: Async & Promises
console.log('A');
setTimeout(() => {
console.log('B');
}, 0);
Promise.resolve().then(() => {
console.log('C');
});
console.log('D');
In what order are the letters logged?
A) A, B, C, D
B) A, C, B, D
C) A, D, C, B
D) A, D, B, C
✓ Correct Answer: C) A, D, C, B
Explanation: A and D are logged synchronously.
Promise callbacks (C) run as microtasks before setTimeout callbacks (B), which are macrotasks.
Question 5: Testing
A test checks that a function returns 42 by logging the value and manually verifying it in the console.
Why is this test considered ineffective?
A) Console logs are ignored by the JavaScript engine.
B) It doesn’t use an assertion and cannot be automated.
C) Tests are not allowed to log to the console.
D) Unit tests must always use async/await.
✓ Correct Answer: B) It doesn’t use an assertion and cannot be automated.
Explanation: Effective tests use assertions so they can run automatically and fail the build when behavior changes. Relying on manual inspection of console output is not reliable or scalable.
💡 Exam Tip: When multiple answers “work”, pick the option that uses modern JS patterns (ES6+, clean code, reusable functions, async/await, testing best practices) rather than older or hacky approaches.
📚 Study Plan for JavaScript Developer I (3–6 Weeks)
🎯 Suggested Roadmap
Focus on Variables, Types, Collections and Objects, Functions, Classes. Use MDN and Trailhead cert-prep badges to solidify basics with hands-on code.
Build small apps that manipulate the DOM, handle events, and call APIs with fetch + async/await. Inspect everything in browser dev tools.
Install Node.js, run basic scripts, and experiment with a test framework (like Jest or similar). Write tests for pure functions, including async ones.
Take practice exams under timed conditions. For each wrong answer, categorize by domain (Variables, Objects, Browser, Async, etc.) and build a small code example to fix the gap.
💡 Exam Day Tips (JavaScript Developer I)
60 questions in 105 minutes ≈ ~1.75 minutes per question. If you’re stuck, mark the question and move on—don’t burn 5 minutes on a single item.
Pay attention to scope, hoisting, async behavior, and small differences like == vs ===,
or let vs var.
When two solutions work, choose the one using modern syntax (ES6+), clear separation of concerns, and good testing or error-handling practices.
❓ JavaScript Developer I – Frequently Asked Questions (FAQ)
Do I need Platform Developer I before JavaScript Developer I?
No. There is no formal prerequisite for JavaScript Developer I. However, many candidates find it useful to have basic Salesforce platform knowledge and some exposure to LWC.
How much pure JavaScript vs Salesforce-specific content is on the exam?
The majority of the exam is about core JavaScript language topics: variables, functions, classes, browser APIs, async, Node.js, and testing. A smaller portion references Salesforce use cases (for example, using JS in LWC), but you don’t need deep Salesforce admin knowledge.
Which resources should I use to prepare?
Start with the official exam guide, then work through the Trailhead JavaScript Developer I cert prep modules and MDN Web Docs for language fundamentals. Add reputable practice exams to get used to timing and question style.
Is this exam only for front-end developers?
No. The certification is for anyone using JavaScript in the web stack, including front-end, back-end, and full-stack developers. Server-side JS (like basic Node.js) is part of the exam.
How do I maintain my JavaScript Developer I certification?
Like other Salesforce certs, you maintain it by completing release maintenance modules on Trailhead when they’re available. These are short, free modules that cover new features and changes.