The const keyword is a way for you to convey that this data should never be changed. As a code base grows, it is easy that changes happen by mistake; such a mistake might be costly. To get compile time support for this, the const keyword is there to help you. Use it in the following way:

const PI = 3.14;
PI = 3 // not allowed

The compiler will even indicate that this is not allowed with the following message:

Cannot assign to PI because it is a constant or a read-only property

A word of caution here: this works only on the top level. You need to be aware of this if you declare objects as const, like so:

const obj = {
  a : 3
}
obj.a = 4; // actually allowed

Declaring the obj const does not freeze the entire object from being edited, but rather what obj points to. So, the following would not be allowed:

obj = {}

Here, we actively change what obj points to, not one of its child properties, therefore it is not allowed and you get the same compile error as earlier.