25 Unnoticeable Features of JavaScript

Often, as developers, we write similar types of code, falling into a pattern that, while comfortable, can sometimes feel mundane.

However, the world of JavaScript is vast, filled with advanced features that, when discovered and used, can transform our development work into something much more exciting and fulfilling.

In this guide, we will unveil 25 advanced JavaScript features that promise not just to reveal these hidden gems but also to elevate your mastery of JavaScript to unprecedented levels.

Let’s embark on this journey of discovery together, integrating JavaScript’s advanced capabilities into our coding repertoire to create more efficient, elegant, and powerful applications. It’s time to infuse our development tasks with a newfound sense of fun and creativity.

1 — Labels for Loop and Block Statements

JavaScript allows labeling loops and block statements, enabling precise control with break and continue.

outerLoop: for (let i = 0; i < 5; i++) {
    innerLoop: for (let j = 0; j < 5; j++) {
        if (i === 2 && j === 2) break outerLoop;
        console.log(`i=${i}, j=${j}`);
    }
}

2 — Comma Operator

The comma operator allows multiple expressions to be evaluated in a sequence, returning the last expression’s result.

let a = (1, 2, 3); // a = 3

3 — Tagged Template Literals Beyond String Formatting

Beyond creating strings, tagged templates can be used for DSLs (Domain Specific Languages), sanitizing user input, or localization.

function htmlEscape(strings, ...values) {
    // Example implementation
}

4 — Function Declarations Inside Blocks

Though not recommended, JavaScript allows function declarations inside blocks, which can lead to different behaviors in non-strict mode.

if (true) {
    function test() { return "Yes"; }
} else {
    function test() { return "No"; }
}
test(); // Behavior varies depending on the environment

5 — void Operator

The void operator evaluates any expression and then returns undefined, useful for hyperlinks with JavaScript.

void (0); // returns undefined

6 — Bitwise Operators for Quick Math

Bitwise operators, like | and &, can perform some math operations much faster, though at the cost of readability.

let floor = 5.95 | 0; // Fast way to do Math.floor(5.95)

7 — with Statement for Working with Objects

The with statement extends the scope chain for a block, allowing you to write shorter code. However, it's not recommended due to readability and performance concerns.

with(document.getElementById("myDiv").style) {
    background = "black";
    color = "white";
}

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8 — Automatic Semicolon Insertion (ASI)

JavaScript tries to fix missing semicolons, but relying on it can lead to unexpected results.

let x = 1
let y = 2
[x, y] = [y, x] // Without proper semicolons, this could fail

9 — in Operator for Property Checking

Check if an object has a property without accessing its value directly.

"toString" in {}; // true

10 — instanceof vs. typeof

instanceof checks the prototype chain, while typeof returns a string indicating the type of the unevaluated operand.

function Person() {}
let person = new Person();
console.log(person instanceof Person); // true
console.log(typeof person); // "object"

11 — Block-Level Functions in ES6

ES6 allows functions to be block-scoped, similar to let and const.

{
    function test() {
        return "block scoped";
    }
}
console.log(typeof test); // "function" in non-strict mode, "undefined" in strict mode

12 — Debugger Statement

Use the debugger statement to pause execution and open the debugger.

function problematicFunction() {
    debugger; // Execution pauses here if the developer tools are open
}

13 — eval() for Dynamic Code Execution

eval executes a string as JavaScript code but comes with significant security and performance implications.

eval("let a = 1; console.log(a);"); // 1

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14 — Non-standard __proto__ Property

While __proto__ is widely supported for setting an object's prototype, it's non-standard. Use Object.getPrototypeOf() and Object.setPrototypeOf() instead.

let obj = {};
obj.__proto__ = Array.prototype; // Not recommended

15 — document.write() for Direct Document Editing

document.write() directly writes to the HTML document, but using it can have negative implications, especially for loading external scripts synchronously.

document.write("<h1>Hello World!</h1>");

16 — Chained Assignment

JavaScript allows for chained assignments, which can assign a single value to multiple variables in one statement.

let a, b, c;
a = b = c = 5; // Sets all three variables to the value of 5

17 — The in Operator for Property Existence

The in operator checks if a property exists within an object without accessing the property value.

const car = {
    make: 'Toyota',
    model: 'Corolla'
};
console.log('make' in car); // true

18 — Object Property Shorthand

When assigning properties to an object, if the property name is the same as the variable name, you can use the shorthand.

const name = 'Alice';
const age = 25;
const person = { name, age };

19 — Default Parameter Values and Destructuring Combined

You can combine default parameter values with destructuring in function parameters for more readable and flexible function definitions.

function createPerson({ name = 'Anonymous', age = 0 } = {}) {
   console.log(`Name: ${name}, Age: ${age}`);
}
createPerson({ name: 'Alice' }); // Name: Alice, Age: 0
createPerson(); // Name: Anonymous, Age: 0

20 — Using Array.fill() to Initialize Arrays

Quickly initialize an array with a specific value using the fill() method.

const initialArray = new Array(5).fill(0); // Creates an array [0, 0, 0, 0, 0]

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21 — Array.includes() for Presence Check

Easily check for the presence of an element within an array with the includes() method, which is more readable than using indexOf().

const fruits = ['apple', 'banana', 'mango'];
console.log(fruits.includes('banana')); // true

22 — Destructuring Aliases

When destructuring an object, you can assign properties to variables with different names using aliases.

const obj = { x: 1, y: 2 };
const { x: newX, y: newY } = obj;
console.log(newX); // 1

23 — Nullish Coalescing Operator for Default Values

Use ?? to provide default values only when dealing with null or undefined, not other falsy values like

const count = 0;
console.log(count ?? 10); // 0, because count is not null or undefined

24 — Dynamic Function Names

Create functions with dynamic names using computed property names in object literals.

const dynamicName = 'func';
const obj = {
    [dynamicName]() {
        return 'Dynamic Function Name!';
    }
};
console.log(obj.func()); // "Dynamic Function Name!"

25 — Private Class Fields

Use the hash # prefix to define private fields in a class, which cannot be accessed from outside the class.

class Counter {
    #count = 0;

    increment() {
        this.#count++;
    }

    getCount() {
        return this.#count;
    }
}

Wrap Up

As we conclude our exploration of the 25 advanced JavaScript features, JavaScript’s arsenal is both vast and profoundly capable.

Each feature we’ve delved into opens up new avenues for solving coding challenges, akin to adding an innovative tool to our toolkit.

This not only enhances our ability to craft solutions creatively and efficiently but also underscores the dynamic versatility of JavaScript.

These advanced features spotlight the critical role of continuous learning in the realm of web development.

Embracing these nuances and integrating them into our daily coding practices allows us to refine our skills and contribute to the evolution of web technologies.

Remember, the path to mastering JavaScript is a continuous journey, where every line of code presents an opportunity to uncover something extraordinary.

Let’s keep pushing the boundaries of what we can achieve with JavaScript, staying curious and open to the endless possibilities that lie ahead.

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