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JavaScript JavaScript Loops, Arrays and Objects Tracking Data Using Objects Mixing and Matching Arrays and Objects

Sandra Vu
Sandra Vu
3,525 Points
Posted by Sandra Vu
Sandra Vu
3,525 Points

" in square bracket notation?

I read the references on StackOverflow and W3 :

obj.["key"]

Code challenge only accepts obj.[key]?

When to use "?

1 Answer

Tim Renner
Tim Renner
11,163 Points

Hi there, you would want to use quotes to hardcode the name of the key. So in your example obj["key"] makes sense if the object is defined with a key named "key". Here are two equivalent ways to access that property:

const obj = {"key": "someValue"};
console.log(obj.key); //someValue
console.log(obj["key"]); //someValue

Bracket notation will evaluate what's in the bracket. Now key can be a variable:

const obj = {"name": "someValue"};
const key = "name";
console.log(obj[key]); // someValue
console.log(obj["key"]); //undefined -- because no property is named "key"

I don't recommend the following, but literals in brackets can allow you to access keys with spaces in them:

const obj = {"what she said": "ermahgerd"};
console.log(obj["what she said"]; //ermahgerd
console.log(obj.what she said); //error -- obj.what is undefined

Also see Mozilla docs on property accessors