Are Trailing Commas in JavaScript Arrays and Objects Officially Supported?

Trailing Commas in Arrays and Objects: A Standards Debate

Trailing commas have become a common sight in JavaScript code, but are they truly a part of the language specification? This question has sparked discussions and concerns among developers, particularly in the context of older browsers like Internet Explorer 8 not supporting them.

Specification Overview

According to ECMAScript 5 (ES5) and ECMAScript 3 (ES3) specifications:

• Objects: Trailing commas are permitted in object literals according to ES5 (section 11.1.5). However, this feature was not present in ES3.
• Arrays: Trailing commas are also allowed in array literals in both ES5 and ES3 (sections 11.1.4).

Therefore, based on the specifications, trailing commas are indeed part of the JavaScript standard for both objects and arrays.

Notable Aspect

It is worth noting that trailing commas can create unexpected behaviors in older browsers like IE8 and earlier versions. These browsers may throw errors or display unexpected results when encountering trailing commas in code.

Conclusion

Based on the language specifications, trailing commas are a valid and standard feature in JavaScript. However, developers should exercise caution when using them in code that may be targeted for execution in older browsers like IE8, which do not fully support the feature.

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