typestrong / learn-typescript Goto Github PK

does this repo need to be updated for typescript 2.0 release?

Thanks for this great tutorial.

However, I found an issue in the comments about const variables that assumes const variables are immutable. But immutability deals with values, not variables.

Variables declared by const, are not immutable. In other words, const is not about immutability at all. It just says the reference that the variable is pointing to, can't be changed after the assignment. From the MDN:

The const declaration creates a read-only reference to a value. It does not mean the value it holds is immutable—just that the variable identifier cannot be reassigned.

So, this may confuse newcomers and people coming from other languages and they may infer that the following statements are wrong in TypeScript/JavaScript (but they're not):

const arr: number[] = [1, 2, 3];
const obj: Object = {
    name: 'John Doe',
    age: 30,
};

arr.push(4); // Okay - No error
obj['status'] = 'married'; // Okay - No error

It's obvious that the following throw errors, however:

const arr: number[] = [1, 2, 3];
const obj: Object = {
    name: 'John Doe',
    age: 30,
};

arr = [1, 2, 3, 4]; // Error - Assignment to constant variable
obj = const obj: Object = {
    name: 'Jane Doe',
    age: 25,
}; // Error - Assignment to constant variable

I can provide more examples if necessary. Regards.

P.S: I've created a PR that removes the unclarity from the comments.