Why Does Array.prototype.push Return the New Array Length Instead of Useful Data?

Why Array.prototype.push Returns the New Length Instead of Useful Data

Array.prototype.push, introduced in ECMA-262, 3rd Edition, returns a Number representing the new length of the array after elements are appended. This design choice has perplexed developers, as it's not directly useful information.

Historical evidence from TC39's communication channels sheds light on this decision. In JS1.2 (Netscape 4), push was modeled after Perl's function and behaved similar to Perl 4 by returning the last item pushed. However, with JS1.3 (Netscape 4.06), push underwent a change to align with Perl 5 conventions and now returns the new array length.

According to the original jsarray.c source code, this modification was intentional:

/*
 * If JS1.2, follow Perl4 by returning the last thing pushed.  Otherwise,
 * return the new array length.
 */

This design choice may stem from a desire to provide consistency across versions of JavaScript and align with the established Perl 5 behavior. While returning the new length may not be immediately valuable, it does ensure clarity on the size of the array after the push operation.

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