Unveiling the Secrets of Curly Brackets in Variable Declarations

The syntax var { ... } = ..., often encountered in JavaScript add-on SDK docs and Chrome Javascript, may initially seem perplexing. However, it represents a powerful feature known as destructuring assignment.

Destructuring assignment enables efficient value extraction from objects and arrays, assigning them to newly declared variables using object and array literal syntax. Consider the following example:

var ascii = {
    a: 97,
    b: 98,
    c: 99
};

var {a, b, c} = ascii;

This code effectively extracts specific properties (a, b, c) from the ascii object and creates individual variables for each property. This approach streamlines code, eliminating the need for repetitive assignments like:

var a = ascii.a;
var b = ascii.b;
var c = ascii.c;

Similarly, you can utilize destructuring assignment for arrays, as illustrated below:

var ascii = [97, 98, 99];

var [a, b, c] = ascii;

This code is equivalent to the following:

var a = ascii[0];
var b = ascii[1];
var c = ascii[2];

Furthermore, destructuring assignment allows for property renaming during extraction. For instance:

var ascii = {
    a: 97,
    b: 98,
    c: 99
};

var {a: A, b: B, c: C} = ascii;

This code creates variables A, B, and C with values corresponding to the properties a, b, and c in the ascii object.