What is Array Destructuring Assignment in JavaScript and Why is it Not Supported by Older Browsers?

Understanding Array Destructuring Assignment: [ (...) ] = (...) in JavaScript

In JavaScript, developers may encounter code snippets like the following:

var myList = [ 1, 2, 3 ];
var a, b, c;

[ a, b, c ] = myList;

This use of square brackets on the left-hand side of variable assignment raises questions about its validity and compliance with JavaScript standards.

Explanation and Compatibility

This code utilizes a feature called destructuring assignment, introduced in JavaScript 1.7 and subsequently standardized in ECMAScript 6. Destructuring assignment allows convenient extraction of values from arrays or objects into individual variables.

Unfortunately, this feature is not part of ECMAScript 5, which explains its compatibility issues with some older browsers, such as Opera 10.60 and Chrome.

Source of Confusion

The use of square brackets on the left-hand side of the assignment could lead to confusion, as it is typically associated with array assignment, e.g., [1, 2, 3] = myList. However, in the context of destructuring, these square brackets serve a different purpose, indicating the target variables for extraction.

Conclusion

Destructuring assignment is a useful feature in JavaScript, but it is important to note its limitations regarding browser compatibility. For code that must support older browsers, it is recommended to avoid using destructuring assignment or provide alternative implementations.

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