How to Add ID to Element Using JavaScript

Adding a unique identifier to HTML elements enables easier styling, DOM access, event handling and overall control in JavaScript web development. This comprehensive guide will teach multiple techniques to assign ID attributes.

The Role and Purpose of IDs

Before jumping into the code, let‘s examine why IDs matter in JavaScript:

Quick Element Access

Retrieving an element by its ID provides the fastest lookup speed compared to other selectors:

document.getElementById(‘header‘);

Since IDs must be unique per page, this will always return one matching element.

Styling Hooks

CSS rules can target IDs without affecting other elements:

#header {
  /* Styles for #header */
}

This allows styling certain parts of UI differently.

Event Handling

Attaching click handlers or other events is simplified with IDs:

const button = document.getElementById(‘submit‘);
button.addEventListener(‘click‘, handleSubmit); 

Componentization

IDs help build encapsulated components like accordions:

<div id="accordion">
  <div id="panel-1">...</div>
  <div id="panel-2">...</div>
</div>

Controlling state relies on unique IDs per component.

Fragment Links

Direct links to sections via ID attributes:

<a href="#features">See Features</a> 

<div id="features">...</div>

So in summary, IDs open up more possibilities in JavaScript interactivity and behavior.

Selecting Elements by ID

Let‘s explore the primary methods for getting element references using IDs:

getElementById()

This handy method looks up one unique element by its ID:

const header = document.getElementById(‘page-header‘); 

With browser support as far back as IE6, this method can be relied on in virtually any project.

Performance

Looking up by ID is quite fast compared to other DOM queries since it directly accesses that element without traversing all nodes.

So reach for getElementById when an element needs frequent accessing.

querySelector()

The querySelector method accepts CSS selector syntax, including IDs prefixed with #:

const header = document.querySelector(‘#page-header‘);

This provides a versatile way to fetch elements that works similarly across modern browsers.

Differences

The key distinction versus getElementById() is:

• querySelector returns first match
• getElementById returns one specific match

So if the ID is meant to be unique, prefer the direct getElementById approach for speed and accuracy.

ID vs Class in JavaScript

Developers often wonder whether to identify elements with IDs or classes. Let‘s compare them:

	ID	Class
Uniqueness	Only 1 per document	Multiple allowed per page
Accessibility	getElementById()	getElementsByClassName()
Selection Speed	Very fast (# direct access)	Slower (traverses all elements)
Styling Hook	High CSS specificity	Lower specificity

So in summary:

• Use IDs for one-off important elements that need frequent JavaScript access or styling hooks.
• Use Classes for groups of elements to be styled or manipulated together.

Combining both techniques as needed is common on robust sites.

Adding IDs to New Elements

When generating elements in JavaScript, assign the ID right away:

During Creation

// Create element
const div = document.createElement(‘div‘);

// Add ID 
div.id = ‘content‘;

With setAttribute()

const div = document.createElement(‘div‘); 
div.setAttribute(‘id‘, ‘content‘);

Using the id property directly sets the identifier in fewer lines.

In Template Literals

Template literals provide an easy way to include IDs in markup:

const html = `  
  <div id="header"></div>
`; 

This declarative syntax clearly conveys the desired ID name.

So new elements can have IDs assigned through multiple JavaScript techniques. Next let‘s see how existing markup can be updated.

Adding ID to Existing Element

To add identifier attributes to markup already on the page:

Step 1: Get Element Reference

Use any of the DOM traversal techniques:

// By tag name  
const div = document.getElementsByTagName(‘div‘)[0];

// By class name
const div = document.getElementsByClassName(‘header‘)[0]; 

// By CSS selector  
const div = document.querySelector(‘.header‘);  

This provides element access for manipulation.

Step 2: Add ID

With the reference, directly set the id property:

div.id = ‘main-header‘;  

Or use setAttribute():

div.setAttribute(‘id‘, ‘main-header‘);  

And the ID is now assigned to existing content!

Semantic ID Values

With so much power comes responsibility. Make ID names descriptive for good semantics:

✅ Do

• site-header
• main-content
• submit-btn

❌ Don‘t

• div1
• blue
• jq372

Well-chosen identifiers improves understanding and avoids obfuscation.

DOM Traversal for Existing Elements

We briefly covered getting access to elements for ID assignment. Let‘s explore those DOM traversal techniques further:

getElementById()

If a unique ID already exists, directly select it:

const header = document.getElementById(‘header‘);

getElementsByTagName()

Gets all elements matching the tag name:

const divs = document.getElementsByTagName(‘div‘); 

Access via index values:

divs[0]; // First div

getElementsByClassName()

Similar to above but using the CSS class name instead:

const boxes = document.getElementsByClassName(‘box‘); 

boxes[1]; // Second box

querySelectorAll()

Returns static nodeList using any CSS selector:

const boxes = document.querySelectorAll(‘.box‘); 

So those are handy methods for selecting existing markup elements to manipulate further.

IDs in JavaScript Frameworks

Let‘s analyze how popular frameworks utilize IDs under the hood:

React

React uses IDs heavily for its reconciliation algorithm:

<div id="header">
  {/* children */} 
</div>   

It depends on element uniqueness during re-renders.

Vue

Vue recommends usage of ID and ref attributes for access:

<div id="header" ref="header">
  <!-- ... -->
</div>

Template and component logic can now target #header.

So while not always explicitly needed in those frameworks, ID values remain quite useful.

Potential Performance Impacts

While extremely useful in JavaScript, improperly using IDs can have downsides:

• Overusing IDs when unnecessary can cause page bloat
• Lots of getElementById lookups with long IDs can have computational burden

Weigh their need on a case-by-case basis. Use classes instead if IDs seem excessive.

Events and IDs

Alongside DOM access, IDs provide huge value for attaching events:

// Get element 
const button = document.getElementById(‘submit‘);  

// Add click handler
button.addEventListener(‘click‘, () => {
  // Handle submit logic...
});

That button can now perform actions when clicked. Direct event binding relies on unique identifiers.

Styling IDs with CSS

The high specificity of ID selectors becomes very useful in CSS:

/* Element with id="submit" */
#submit { 
  background-color: blue;
}  

/* Override button defaults */  
button {
  padding: 10px 15px; 
  background: none;
}

The #submit rules take priority regardless of the tag name.

Cleaning Up IDs Dynamically

When generating lots of elements dynamically, be sure to avoid ID collisions:

let count = 1;

elements.forEach(() => {
  // Append element
  const el = createElement();  

  // Add unique ID  
  el.id = `el-${count}`;
  count++;

  // ...
});

Incrementing variables keeps identifiers distinct.

Proper cleanup is also important on removal:

function removeElement(id) {

  const el = document.getElementById(id);  

  // Clear reference
  el.id = ‘‘; 

  // Remove from DOM
  el.remove();

}

This avoids hassles if dynamically recreating same components.

ES6 ID Techniques

With ES6 destructuring and syntax, IDs can be assigned concisely:

Shorthand Properties

const el = document.createElement(‘div‘);
el.id; // ID assigned

Arrow Functions

elements.forEach(el => {
  el.id = getId(); 
});

let and const

const id = ‘header‘;
let newId = ‘content‘; 

So while not revolutionary changes, ES6 provides some nice quality-of-life improvements for working with IDs.

Best Practices for JavaScript IDs

To recap effective usage of IDs:

• Semantic Names like site-header
• Only When Needed instead of defaulting to them
• Use for Individual Elements instead of groups
• Keep Short enough to avoid performance issues
• Globally Unique across the entire document
• Use camelCase naming convention for multi-word

Following these simple tips will improve code efficiency and understanding.

Conclusion

This guide provided a thorough exploration of assigning ID attributes to HTML elements using native JavaScript.

The key highlights include:

• Purpose – Enable easier access, styling hooks and componentization
• Adding IDs – Via properties, setAttribute(), or declaratively in templates
• Selecting Elements – Techniques like getElementById and DOM traversal
• IDs vs. Classes – Difference in uniqueness and DOM lookup performance
• Best Practices – Semantic names, moderate usage, short length

With this foundation, harnessing the power of IDs should now feel less mysterious. Refer to this article anytime guidance is needed for adding identifiers effectively in your JavaScript projects.

Please reach out with any other questions!