Dollar Sign in JavaScript: A Comprehensive Guide

If you are a JavaScript developer, you might have wondered what the dollar sign ($) means in JavaScript code. Is it a special symbol, a function, or a variable? And how can you use it in your own projects?

In this blog post, I will answer these questions and explain the meaning and usage of the dollar sign in JavaScript. I will also show you some examples of how the dollar sign can make your code more concise and readable.

By the end of this post, you will have a better understanding of this common JavaScript feature and how to leverage it for your benefit.

What is the Dollar Sign in JavaScript?

In JavaScript, the dollar sign ($) is a valid character that can be used in variable names, function names, and more. It's not a reserved keyword, and its use is entirely optional. The dollar sign doesn't have any special meaning in the JavaScript language itself.

In JavaScript, it gained popularity through libraries like jQuery, where it was used as a shorthand for the jQuery function.

While the dollar sign is not a language feature, it's still used in some JavaScript libraries and frameworks.

How to Use the Dollar Sign in JavaScript

1. How to write and include the dollar sign in JavaScript code

To use the dollar sign in JavaScript, you simply include it in variable or function names:

var myVariable$ = 40;

2. Role of the dollar sign in jQuery and other libraries

In jQuery, the dollar sign is used as a shorthand for the jQuery function, making it easier to select and manipulate DOM elements:

var element = $('#myElement');

In plian JavaScript, you have to write it like:

var element = document.getElementById('#myElement');

3. Escaping the dollar sign in JavaScript

If you want to use a dollar sign as a regular character and not as a special symbol, you can escape it using a backslash ($):

var escaped = 'This is a dollar sign \$';
console.log(escaped)
// Output: This is a dollar sign: $

You can use backslash to escape special characters in a string, but it is not mandatory. For example, if you use a JavaScript template literal (backtick) to create a string, and you have a $ sign followed by an open curly brace, you will get an error saying "Unterminated string literal".

This is because the template literal expects an expression inside the curly braces, but it does not find one. To avoid this error, you can either use a backslash before the $ sign, or use a different type of quotation mark for the string.

var escaped = `This is a dollar sign: ${`;
console.log(escaped)
// ERROR: Unterminated string literal

The Dollar Sign in JavaScript Variables

While using the dollar sign in JavaScript variable names is allowed, it's not a common practice in modern JavaScript development.

You can use it for special cases, like when dealing with jQuery or legacy code.

You may choose to use the dollar sign in variable names to indicate special significance or association with specific libraries or frameworks.

It's generally recommended to avoid using the dollar sign in variable names to maintain code readability.

Descriptive variable names are preferred for better code comprehension.

Functions and the Dollar Sign in JavaScript

You can also use the dollar sign ($) in function names:

function calculateTotal$() {
    // function logic here
}

Using the dollar sign in function names can make it clear that a function is related to a specific feature or library.

Overusing the dollar sign in function names can lead to confusion, so it should be used judiciously.

Code examples demonstrating function usage

function displayPrice$(price) {
    console.log(`Price: $${price}`);
}

displayPrice$(99.99); 
// Output: Price: $99.99

Displaying a Dollar Sign in JavaScript

1. Displaying a dollar sign in output

To display a dollar sign in JavaScript output, you can simply include it within strings or use it as part of formatting:

var price = 50;
console.log('The price is: $' + price);

// Using template literals (ES6)
console.log(`The price is: $${price}`);

Both command will print the same output.

The price is: $50

2. Formatting numbers with dollar signs and commas

To format numbers with dollar signs and commas, you can use the toLocaleString() method:

var amount = 1000;
var options = { style: 'currency', currency: 'USD' }
var formattedAmount = amount.toLocaleString('en-US', options);
console.log(formattedAmount); 
// Output: $1,000.00

Dollar sign display is often required when working with financial or monetary values, such as displaying prices, costs, or budgets in an application.

The Dollar Sign in JavaScript ES6

With the introduction of ES6, the dollar sign remains a valid character in variable and function names:

const total$ = 100;
const calculateTotal$ = () => {
    // Function logic here
};

ES6 doesn't introduce any special functionality related to the dollar sign.

ES6 introduces constand letfor JavaScript variable declaration. You can use these keywords along with the dollar sign as needed.

ES6 features, including the use of the dollar sign, are widely supported in modern browsers and JavaScript environments. Ensure you're using an up-to-date JavaScript engine for maximum compatibility.

Common Misconceptions

Some developers believe that the dollar sign has built-in functionality in JavaScript, which is not true. It's a character like any other.

The dollar sign's role in JavaScript is not predefined by the language but is often used in libraries and frameworks. Understanding this can prevent confusion and help you make informed coding decisions.

Alternatives to the Dollar Sign

While the dollar sign is one option, there are alternatives for variable naming in JavaScript, such as underscores (_) or camelCase notation.

Each alternative character has its advantages and disadvantages, and the choice often depends on coding style and project requirements.

Practical Examples

Let's explore some practical examples that showcase when and how the dollar sign can be used effectively in JavaScript. We'll cover scenarios like manipulating DOM elements with jQuery and formatting currency values.

Using jQuery with the dollar sign

// Select an element with the ID "myElement" using jQuery
var element = $('#myElement');

// Hide the selected element
element.hide();

Formatting currency with the dollar sign

The following JavaScript code defines a function formatCurrency$ that takes a numeric amount. Returns a string formatted as a currency with two decimal places using JavaScript toFixed() function.

function formatCurrency$(amount) {
    return `$${amount.toFixed(2)}`;
}

var price = 19.99;
console.log(`Total cost: ${formatCurrency$(price)}`);

Conclusion

To wrap up, we have learned what the dollar sign means in JavaScript and how it is used in different contexts. We have seen that it can be a valid identifier, a shorthand for document.getElementById(), a jQuery object, or a template literal delimiter.

We have also explored some of the benefits and drawbacks of using the dollar sign in our code.

Hopefully, this article has helped you understand this versatile symbol better and how to use it effectively in your projects.

Comments

[Peter Vivo]

Current days the qwik use $ sign for a good reason:

What are all those $ signs?

You might have noticed there are more $ signs than usual in Qwik apps, such as: component$(), useTask$(), and

console.log('click')} />. It serves as a marker for a lazy-load boundary. Qwik breaks your application into small chunks; these pieces are smaller than the component itself. For event handlers, hooks, etc. The $ signals to both the optimizer and the developer when it's happening.

Example:

import { component$ } from '@builder.io/qwik';

export default component$(() => {
  console.log('render');
  return <button onClick$={() => console.log('hello')}>Hello Qwik</button>;
});

source

[Raja MSR]

Thanks @pengeszikra for sharing the reference. Unless there is a need, no need to use $ sign in variable and function names.