Difference Between null & Undefined and =, == & === | Peoplewoo Skills

What is null in JavaScript?

null is an assignment value. It represents the intentional absence of an object value. Developers explicitly assign null when they want to clear or reset a variable.

Example:

 let x = null; console.log(x); // null 

In LWC, null is commonly used to reset tracked variables or remove reference values.

Difference Between null and undefined

The following table explains the core differences:

Difference Between =, ==, and ===

JavaScript provides three different operators for assignment and comparison. Understanding these is essential for writing bug-free LWC code.

Examples:

 // Assignment let x = 10; // Loose equality (value only) console.log(5 == "5");

  // true // Strict equality (value + type) console.log(5 === "5");

 // false console.log(5 === 5);   // true 

In Lightning Web Components, always prefer === to avoid unexpected behavior, especially when validating API inputs or comparing values returned from Apex.

Real-Life Example in LWC

Imagine you are fetching user details from an Apex method. Initially, the variable will be undefined because the result hasn't arrived. After data is loaded, if a field is missing, it may return null.

 @track userDetails; connectedCallback() {     getUserInfo()         

.then(result => {             if(result === null) {            

     console.log("No user data found");             }         

    this.userDetails = result;         }); } 

Best Practices

• Use === for all comparisons.
• Use null intentionally when resetting values.
• Avoid unnecessary type coercion caused by ==.
• Always initialize variables properly in LWC.
• Check for both null and undefined where needed using:

  if (value == null)

  It covers both cases.