yes that is obvious - my point was that the functionality is minimal. with guards:

    const at = (arr, i) => {
      if(!(Array.isArray(arr) && typeof i === 'number')) {
        throw new Error('invalid arguments');
      }
      // same as before
    };

you wouldn't just commit a single-line function in your code. But there are 10,000 micro-functions that could be in the core of JS. Why bother to add this, especially if it's so easy to implement? There are surely better things the JS committee could be putting their time towards, like providing functionality that is presently lacking in JS (maybe they could finally get around to advancing the pipe operator through the TC stages).