asuming that a "const" is constant, I wouldn't have thought that this is possible:
const obj = { key1: value1, key2: value2 }; obj["key3"] = value3; obj.key4 = value4; Can somebody explain it to me?
1 Answer
In your case, you aren't actually changing obj. You're just changing a property of obj, so it isn't considered like you're trying to change a constant.
Only doing this is problematic:
const obj = { key1: value1, key2: value2 }; obj = 5 
7 Comments
Pointy
Why would this be downvoted? It's the correct answer.
isaacsan 123
@Pointy I don't know. 😬
divillysausages
Small addition: if you want to make the actual properties of the Object
const, look into Object.freeze: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/…isaacsan 123
@divillysausages Oh snap, I didn't know that! That's really cool. Thanks for the addition.
3limin4t0r
Note that freezing an object is shallow. If the object contains nested objects they are not frozen. eg.
obj = { a: 1, b: { c: 2 } } then obj.a = 3 results in an error, but obj.b.c = 3 is still allowed. (only obj is frozen, obj.b is not) |
const"variable" is a variable that cannot be re-assigned to another value once created. By mutating the object the variable still holds the same reference, so the variable did not change.objto be immutablevalue1-value4are not defined. Changing them to strings resolves this. But the most likely reason for the downvotes is probably the lack of research. If you searched "JavaScript why can I change a const" using any search engine, you would probably find an answer. I personally don't find the question downvote worthy, but I assume others might disagree.