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JavaScript\u2019s come a long way, and if you\u2019re aiming for a JavaScript developer job in Singapore<\/strong><\/a>, it\u2019s no longer enough to just \"know the basics.\" Technical interviews today aren\u2019t about textbook answers \u2014 they\u2019re about showing you can think in clean, scalable JavaScript<\/strong>. Concepts like destructuring assignment<\/strong>, async\/await<\/strong>, and choosing between let vs const<\/strong> aren\u2019t just nice-to-know skills anymore \u2014 they're expected as part of strong JavaScript interview preparation<\/strong>.<\/a><\/p>\r\n\r\n\r\n\r\n This guide breaks down the most important ES6+ JavaScript features<\/strong> that show up over and over again in real-world interviews \u2014 explained simply, with examples you\u2019ll actually remember. One of the foundational changes introduced in ES6 was the new ways to declare variables using In modern JavaScript, the evolution from Pro Tip:<\/strong> Always default to Common Mistake:<\/strong> Developers often think Related Read: 100+ Node.js Interview Questions and Answers [ 2026 ]<\/a><\/strong><\/p>\n\n\n\n Arrow functions, introduced in ES6, offer a concise syntax for writing function expressions. They are not just syntactic sugar \u2014 they have important behavioral differences, especially regarding the If the function body contains only a single expression, the braces and Arrow functions do not bind their own Pro Tip:<\/strong> Use arrow functions for non-method callbacks like Common Mistake:<\/strong> Accidentally using arrow functions for object methods where Template literals are one of the most loved ES6 features that simplify string operations significantly. Instead of tedious concatenations, you can now create strings that are dynamic, readable, and multi-line.<\/p>\n\n\n\n Enclosed by backticks (“ ` “), template literals allow embedded expressions inside Template literals automatically handle multi-line strings without needing escape characters like Besides variables, you can insert any valid JavaScript expression inside template literals.<\/p>\n\n\n\n Pro Tip:<\/strong> Template literals are particularly powerful in generating dynamic HTML structures when working with frontend JavaScript frameworks.<\/p>\n\n\n\n Common Mistake:<\/strong> Forgetting to use backticks (“ ` “) and mistakenly using single or double quotes (” or ‘) results in a syntax error when trying to interpolate variables.<\/p>\n\n\n\n Related Read: React JS Interview Questions and Answers [ 2026 ]<\/a><\/strong><\/p>\n\n\n\n Destructuring allows you to extract values from arrays and objects, making your code shorter and more readable. It\u2019s frequently tested in programming interviews<\/strong>, particularly for developers applying for Java Developer Jobs<\/strong>.<\/a><\/p>\n\n\n\n Extract array elements into variables based on position.<\/p>\n\n\n\n Extract properties based on their key names.<\/p>\n\n\n\n Access deeply nested properties easily.<\/p>\n\n\n\n Use default values during destructuring to handle cases where the property might be undefined.<\/p>\n\n\n\n Forgetting to use the correct key name when destructuring objects results in Related Read: HTML and CSS Interview Questions & Answers [ 2026 ]<\/a><\/strong><\/p>\n\n\n\n The spread ( Expands elements of an array or object into individual elements.<\/p>\n\n\n\n Collects remaining elements into an array or object.<\/p>\n\n\n\n Use the spread operator to clone arrays and objects without affecting the original data \u2014 especially critical in functional programming and React state management.<\/p>\n\n\n\n Confusing spread and rest syntax: both use —<\/p>\n\n\n\n Read Also: Most Asked Cypress Interview Questions<\/a><\/strong><\/p>\n\n\n\n Default parameters allow you to specify default values for function arguments if no value or Combine default parameters with destructuring for maximum power.<\/p>\n\n\n\n Always list parameters with defaults at the end of the parameter list to avoid unexpected behavior.<\/p>\n\n\n\n Misunderstanding default parameters when an argument is passed explicitly as ES6 introduced several enhancements to object literals that make creating and working with objects faster, cleaner, and more powerful. This is crucial for writing modern, maintainable JavaScript code, especially during interviews where clean syntax is evaluated.<\/p>\n\n\n\n If the key and the variable name are the same, you can use shorthand syntax.<\/p>\n\n\n\n You can define functions inside objects without the You can dynamically compute property keys inside objects using square brackets.<\/p>\n\n\n\n Use computed property names for dynamic keys in APIs or configuration objects, which is common in real-world development.<\/p>\n\n\n\n Forgetting to wrap dynamic keys in square brackets results in literal property names instead of evaluated expressions.<\/p>\n\n\n\n Related Read: Front End Developer Interview Questions and Answers [ 2026 ]<\/a><\/strong><\/p>\n\n\n\n Promises and async\/await revolutionized asynchronous programming in JavaScript, replacing callback hell with cleaner, more manageable code structures.<\/p>\n\n\n\n A Promise represents the eventual completion or failure of an asynchronous operation.<\/p>\n\n\n\n Async functions allow you to write asynchronous code that looks synchronous using In interviews, be prepared to explain how Promises work internally, the three states (pending, fulfilled, rejected), and how Forgetting to wrap —<\/p>\n\n\n\n ES6 classes provide a cleaner syntax for creating constructor functions and handling inheritance. Although classes are syntactic sugar over JavaScript\u2019s prototype system, they make code more readable and object-oriented. <\/p>\n\n\n\n Classes and inheritance were introduced to JavaScript with ES6 to bring better structure to code. Understanding these concepts is important in technical interviews. These topics are closely related to concepts seen in advance Java interview questions and answers<\/strong>.<\/a><\/p>\n\n\n\n Subclasses are created using the Interviewers love to ask about how inheritance works under the hood \u2014 be ready to explain the prototype chain even when using class syntax.<\/p>\n\n\n\n Forgetting to call Related Read: Full Stack Developer Skills You Can Add to Your Resume<\/a><\/strong><\/p>\n\n\n\n Before ES6, JavaScript lacked a native module system. Developers relied on external solutions like CommonJS and AMD. ES6 modules finally introduced a standardized way to organize code into reusable pieces, improving code maintainability and scalability.<\/p>\n\n\n\n Developers interviewing for Java jobs<\/strong> <\/a>will likely be asked about modules, especially when working with modern JavaScript applications. Familiarity with ES6 modules is essential, and if you\u2019re interested in work-from-home Java developer jobs<\/a><\/strong>, it\u2019s even more crucial regarding collaboration and module sharing.<\/p>\n\n\n\n You can export functions, objects, or primitives from a module using either named or default exports.<\/p>\n\n\n\n
Whether you\u2019re applying to fast-paced tech startups at LaunchPad One-North<\/strong> or eyeing a role at big players like Shopee<\/strong> and Sea Group<\/strong>, understanding modern JavaScript ES6 features<\/strong> gives you a real advantage.<\/p>\r\n\r\n\r\n\r\n
If you\u2019re serious about standing out and landing that next big opportunity, let\u2019s dive right into the world of JavaScript ES6 interview success<\/strong>.<\/p> <\/p>\n\n\n\nTable of Contents<\/h2>\n\n\n\n
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1. Variable Declarations: var, let, and const<\/h2>\n\n\n\n
let<\/code> and const<\/code> instead of the traditional var<\/code>. Understanding these distinctions is crucial for writing predictable, bug-free JavaScript code.<\/p>\n\n\n\nvar<\/code> to let<\/code> and const<\/code> is vital for writing cleaner code, especially in interviews for Java developers<\/a><\/strong>. These changes help developers avoid common pitfalls and ensure more predictable variable management. If you\u2019re preparing for Java Developer Jobs<\/strong>, understanding variable scoping is crucial<\/p>\n\n\n\n1.1 var<\/h3>\n\n\n\n
var<\/code> declarations are function-scoped, meaning a variable declared with var<\/code> is accessible throughout the enclosing function. If declared outside a function, it becomes globally scoped. It also supports hoisting, but the variable is initialized with undefined<\/code>.<\/p>\n\n\n\nfunction example() \nexample();\n<\/code><\/pre>\n\n\n\n1.2 let<\/h3>\n\n\n\n
let<\/code> is block-scoped, meaning it is only accessible within the nearest pair of curly braces ( <\/code>). It also supports hoisting but does not initialize the variable, leading to a ReferenceError<\/strong> if accessed before declaration (Temporal Dead Zone).<\/p>\n\n\n\n \n<\/code><\/pre>\n\n\n\n1.3 const<\/h3>\n\n\n\n
const<\/code> behaves similarly to let<\/code> with block-scope behavior. However, variables declared with const<\/code> must be initialized at the time of declaration and cannot be reassigned.<\/p>\n\n\n\nconst pi = 3.14;\npi = 3.1415; \/\/ TypeError\n<\/code><\/pre>\n\n\n\nconst<\/code> unless you specifically need to reassign a variable with let<\/code>.<\/p>\n\n\n\nconst<\/code> makes an object immutable. Only the reference is immutable, not the contents. You can still modify the properties of a const<\/code> object.<\/p>\n\n\n\nconst user = ;\nuser.name = \"Bob\"; \/\/ This is allowed\n<\/code><\/pre>\n\n\n\n2. Arrow Functions<\/h2>\n\n\n\n
this<\/code> keyword.<\/p>\n\n\n\n2.1 Syntax of Arrow Functions<\/h3>\n\n\n\n
const add = (a, b) => a + b;\n<\/code><\/pre>\n\n\n\nreturn<\/code> statement can be omitted. For more complex bodies, use braces and a return<\/code> keyword.<\/p>\n\n\n\nconst multiply = (a, b) => ;\n<\/code><\/pre>\n\n\n\n2.2 Behavior of this<\/h3>\n\n\n\n
this<\/code>. Instead, they inherit this<\/code> from the surrounding (lexical) scope. This makes them ideal for callbacks and event listeners in many cases.<\/p>\n\n\n\nfunction Counter() , 1000);\n}\nnew Counter();\n<\/code><\/pre>\n\n\n\n2.3 When Not to Use Arrow Functions<\/h3>\n\n\n\n
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this<\/code> (e.g., in object methods)<\/li>\n\n\n\nmap<\/code>, filter<\/code>, or forEach<\/code> \u2014 they result in cleaner, more maintainable code.<\/p>\n\n\n\nthis<\/code> needs dynamic binding can lead to unexpected behavior.<\/p>\n\n\n\nconst user = `) \/\/ 'this' is not the user object!\n};\nuser.greet(); \/\/ Output: Hello, undefined\n<\/code><\/pre>\n\n\n\n3. Template Literals<\/h2>\n\n\n\n
3.1 Syntax<\/h3>\n\n\n\n
$ <\/code>.<\/p>\n\n\n\nconst name = \"Alice\";\nconsole.log(`Hello, $ !`);\n<\/code><\/pre>\n\n\n\n3.2 Multi-line Strings<\/h3>\n\n\n\n
\\n<\/code>.<\/p>\n\n\n\nconst message = `Hello,\nThis is a\nmulti-line string.`;\nconsole.log(message);\n<\/code><\/pre>\n\n\n\n3.3 Expression Interpolation<\/h3>\n\n\n\n
const a = 5;\nconst b = 10;\nconsole.log(`Sum of a and b is $ `);\n<\/code><\/pre>\n\n\n\nconst name = \"Alice\";\nconsole.log(\"Hello, $ \"); \/\/ Incorrect! Won't interpolate.\n<\/code><\/pre>\n\n\n\n4. Destructuring Assignment<\/h2>\n\n\n\n
4.1 Array Destructuring<\/h3>\n\n\n\n
const numbers = [10, 20, 30];\nconst [first, second, third] = numbers;\nconsole.log(first, second, third); \/\/ 10 20 30\n<\/code><\/pre>\n\n\n\n4.2 Object Destructuring<\/h3>\n\n\n\n
const user = ;\nconst = user;\nconsole.log(name, age); \/\/ Alice 25\n<\/code><\/pre>\n\n\n\n4.3 Nested Destructuring<\/h3>\n\n\n\n
const person = \n};\nconst } = person;\nconsole.log(city); \/\/ New York\n<\/code><\/pre>\n\n\n\nPro Tip:<\/h3>\n\n\n\n
const = user;\nconsole.log(role); \/\/ Guest\n<\/code><\/pre>\n\n\n\nCommon Mistake:<\/h3>\n\n\n\n
undefined<\/code> values.<\/p>\n\n\n\nconst = user;\nconsole.log(username); \/\/ undefined\n<\/code><\/pre>\n\n\n\n5. Spread and Rest Operators<\/h2>\n\n\n\n
...<\/code>) and rest (...<\/code>) operators are powerful tools for working with arrays, objects, and function parameters. They provide flexibility and make the code cleaner and more expressive.<\/p>\n\n\n\n5.1 Spread Operator<\/h3>\n\n\n\n
const arr1 = [1, 2, 3];\nconst arr2 = [...arr1, 4, 5];\nconsole.log(arr2); \/\/ [1, 2, 3, 4, 5]\n\nconst obj1 = ;\nconst obj2 = ;\nconsole.log(obj2); \/\/ \n<\/code><\/pre>\n\n\n\n5.2 Rest Operator<\/h3>\n\n\n\n
const [first, ...others] = [1, 2, 3, 4];\nconsole.log(first); \/\/ 1\nconsole.log(others); \/\/ [2, 3, 4]\n\nfunction sum(...nums) \nconsole.log(sum(1, 2, 3)); \/\/ 6\n<\/code><\/pre>\n\n\n\nPro Tip:<\/h3>\n\n\n\n
Common Mistake:<\/h3>\n\n\n\n
...<\/code>, but spread is used in function calls or literals, while rest is used in function parameters and destructuring assignments.<\/p>\n\n\n\n6. Default Parameters<\/h2>\n\n\n\n
undefined<\/code> is passed.<\/p>\n\n\n\nfunction greet(name = \"Guest\") !`;\n}\nconsole.log(greet()); \/\/ Hello, Guest!\nconsole.log(greet(\"Alice\")); \/\/ Hello, Alice!\n<\/code><\/pre>\n\n\n\n6.1 Why Default Parameters Matter<\/h3>\n\n\n\n
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undefined<\/code> values when parameters are optional<\/li>\n<\/ul>\n\n\n\n6.2 Default Parameters with Destructuring<\/h3>\n\n\n\n
function createUser( = ) is $ years old.`;\n}\nconsole.log(createUser( )); \/\/ Bob is 18 years old\nconsole.log(createUser()); \/\/ Anonymous is 18 years old\n<\/code><\/pre>\n\n\n\nPro Tip:<\/h3>\n\n\n\n
Common Mistake:<\/h3>\n\n\n\n
null<\/code> \u2014 only undefined<\/code> triggers the default value, not null<\/code>.<\/p>\n\n\n\nfunction greet(name = \"Guest\") \ngreet(undefined); \/\/ Guest\ngreet(null); \/\/ null (NOT Guest)\n<\/code><\/pre>\n\n\n\n7. Enhanced Object Literals<\/h2>\n\n\n\n
7.1 Property Shorthand<\/h3>\n\n\n\n
const name = \"Alice\";\nconst age = 25;\nconst user = ;\nconsole.log(user); \/\/ \n<\/code><\/pre>\n\n\n\n7.2 Method Shorthand<\/h3>\n\n\n\n
function<\/code> keyword.<\/p>\n\n\n\nconst user = \n};\nconsole.log(user.greet());\n<\/code><\/pre>\n\n\n\n7.3 Computed Property Names<\/h3>\n\n\n\n
const prop = \"id\";\nconst user = ;\nconsole.log(user); \/\/ \n<\/code><\/pre>\n\n\n\nPro Tip:<\/h3>\n\n\n\n
Common Mistake:<\/h3>\n\n\n\n
8. Promises and Async\/Await<\/h2>\n\n\n\n
8.1 Promises<\/h3>\n\n\n\n
const promise = new Promise((resolve, reject) => );\n\npromise\n .then(result => console.log(result))\n .catch(error => console.error(error));\n<\/code><\/pre>\n\n\n\n8.2 Async\/Await<\/h3>\n\n\n\n
await<\/code> inside an async<\/code> function.<\/p>\n\n\n\nasync function fetchData() catch (error) \n}\nfetchData();\n<\/code><\/pre>\n\n\n\n8.3 Promise Chaining vs Async\/Await<\/h3>\n\n\n\n
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Pro Tip:<\/h3>\n\n\n\n
await<\/code> pauses execution without blocking the thread.<\/p>\n\n\n\nCommon Mistake:<\/h3>\n\n\n\n
await<\/code> calls inside a try\/catch<\/code> block can cause unhandled promise rejections.<\/p>\n\n\n\n9. Classes and Inheritance<\/h2>\n\n\n\n
9.1 Defining a Class<\/h3>\n\n\n\n
class Person \n greet() !`;\n }\n}\nconst person1 = new Person(\"Alice\");\nconsole.log(person1.greet());\n<\/code><\/pre>\n\n\n\n9.2 Inheritance with extends<\/h3>\n\n\n\n
extends<\/code> keyword, allowing child classes to inherit and override methods from parent classes.<\/p>\n\n\n\nclass Animal \n speak() makes a noise.`);\n }\n}\n\nclass Dog extends Animal barks.`);\n }\n}\n\nconst dog = new Dog(\"Buddy\");\ndog.speak(); \/\/ Buddy barks.\n<\/code><\/pre>\n\n\n\n9.3 The super Keyword<\/h3>\n\n\n\n
super()<\/code> is used to call the constructor or methods of the parent class inside a subclass.<\/p>\n\n\n\nclass Cat extends Animal \n}\n<\/code><\/pre>\n\n\n\nPro Tip:<\/h3>\n\n\n\n
Common Mistake:<\/h3>\n\n\n\n
super()<\/code> inside the subclass constructor before using this<\/code> causes a ReferenceError.<\/p>\n\n\n\nclass Car extends Vehicle \n}\n<\/code><\/pre>\n\n\n\n10. Modules: import and export<\/h2>\n\n\n\n
10.1 Exporting<\/h3>\n\n\n\n
\/\/ utils.js\nexport const add = (a, b) => a + b;\nexport const subtract = (a, b) => a - b;\n<\/code><\/pre>\n\n\n\n