mutable

Vndoughtedly constaunce is an honourable vertue, as inconstance is reprochefull and odious. Wherfore that man whiche is mutable for euerye occasyon, muste nedes often repente hym, and in moche repentance is nat only moche foly, but also great detriment: whiche euery wyse man wyll eschue if he can.

A value of a mutable type can change. Objects and arrays are mutable: a JavaScript program can change the values of object properties and array elements. Numbers, booleans, null, and undefined are immutable.