When should I use bracket notation versus dot notation for JavaScript object properties?

[SwiftCoder15]

I’m working with JavaScript objects and I keep getting mixed up about the different ways to access properties. Sometimes I see people using the dot syntax like obj.property and other times they use square brackets like obj['property'].

const userInfo = {
  firstName: 'Alice',
  lastName: 'Johnson',
  age: 28
};

// Both methods seem to work
console.log(userInfo.firstName);
console.log(userInfo['firstName']);

I understand both methods can retrieve the same data, but I’m unsure when to use one over the other. Are there specific situations where brackets are necessary instead of dots? What are the key differences between these two methods, and when should I use each one?

[Liam_25Meditation]

Brackets are a lifesaver for property names with numbers or special characters. You can’t do obj.123name - it’ll error out. But obj['123name'] works perfectly. And if you’re pulling property names from user input or APIs, brackets are pretty much required since you never know what weird names you’ll encounter.

[SwimmingShark]

It’s all about whether you know the property name ahead of time or need to figure it out dynamically. Dot notation is perfect when you know exactly what property you want, but brackets are a lifesaver when you’re working with variables or expressions. I ran into this with API responses that weren’t consistent - sometimes I’d get ‘user_id’, other times ‘userId’. Bracket notation with variables let me handle both without writing separate code for each case. Brackets are also your only choice for numeric properties or reserved words. You can’t write obj.123 or obj.class, but obj[‘123’] and obj[‘class’] work perfectly. Same thing when you’re looping through Object.keys() or using for…in - you’re dealing with property names as strings, so brackets are the way to go. Sure, the syntax looks more verbose, but when you need dynamic property access, it’s your only option.

[Neo_Movies]

It’s all about dynamic property access and weird property names. I hit this building a form validator - the property names came from input fields with hyphens and spaces. You need brackets when the property name is in a variable or has characters that break dot notation. Like ‘user-name’ or ‘first name’ - dot notation just won’t work. Same goes for looping through object properties dynamically. Performance-wise, dot notation’s faster since it compiles, while brackets evaluate at runtime. But honestly, the difference is tiny unless you’re doing something crazy. I use dot notation for regular stuff since it’s cleaner, then switch to brackets when I need the flexibility or I’m stuck with funky property names.