Why does Array.prototype.reduce not have a thisObject parameter?

Question

Javascript Array methods such as forEach have a thisArg parameter, which is used as the context for invoking the callback:

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Answer 1

On the Es-discuss mailing list you find in answer http://article.gmane.org/gmane.comp.lang.javascript.ecmascript4.general/4770

The other methods with callbacks take a 'thisArg' not because it is needed or even useful, but for compatibility, because they already do in existing implementations that provide these functions.