What difference does it makes to parse something as an object literal rather than as a block?

Question

Sorry for my ignorance on JavaScript basic concepts.

It boils down to this:

Literal - A value found directly in the script. Examples:

Answer 1

First, don't eval JSON, use JSON.parse on the String source

---

A block is a "group of expressions" for example,

let x = 0;
if (true) {
    // this is a block
    ++x;
}

However, equally this is also a block

let x = 0;
{ // hi there, I'm a block!
    ++x;
}

This means when the interpreter sees block notation, it assumes a block even if you do something like this

{ // this is treated as a block
    foo: ++x
}

Here, foo acts as a label rather than a property name and if you try to do more complex things with the attempted object literal, you're going to get a Syntax Error.

When you want to write an Object literal ambiguously like this, the solution is to force the interpreter into "expression mode" explicitly by providing parenthesis

({ // this is definately an Object literal
    foo: ++x
})