What are square brackets doing on the left-hand side of variable assignment in JavaScript?

Destructuring Assignment: Uncovering the Meaning of Square Brackets on the Left-Hand Side of Variable Assignment

In JavaScript, encountering square brackets on the left-hand side of a variable assignment may seem perplexing. To decipher the implications of this syntax, we venture into the realms of destructuring assignment.

Syntax and Operation

Destructuring assignment, a feature introduced in JavaScript 1.7 and ECMAScript 6, enables us to unpack values from arrays or objects into distinct variables. Its syntax resembles:

[variable1, variable2, variable3] = [value1, value2, value3];

In the example code:

[ a, b, c ] = myList;

the square brackets on the left-hand side represent destructuring assignment. It assigns the values in the array myList to the variables a, b, and c.

Browser Support

Despite functioning seamlessly in Opera 10.30 and Firefox 3.6.x, destructuring assignment is unsupported in Opera 10.60 and Chrome. This inconsistency is attributed to the fact that destructuring assignment is not part of ECMAScript 5.

ECMAScript Standard Compliance

As verified by the linked reference, destructuring assignment is not compliant with ECMAScript 5. It was introduced as a feature in JavaScript 1.7 and later formalized in ECMAScript 6.

Conclusion

Destructuring assignment, symbolized by square brackets on the left-hand side of variable assignment, provides a concise way of unpacking values from arrays or objects. However, its cross-browser support is limited due to its absence in ECMAScript 5.

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