Editing Array length in a variable versus per-iteration access of array length in a for loop This edit will create a new revision. Your details (optional) Name Email (won’t be displayed; might be used for Gravatar) URL Test case details Title * Published (uncheck if you want to fiddle around before making the page public) Description (in case you feel further explanation is needed)(Markdown syntax is allowed) Storing the length property of an array that will be iterated through with a for loop into a variable is an old school performance optimization for JavaScript. Browsers have since evolved to better handle these sorts of minor optimizations. Interested in seeing whether this optimization is still beneficial in today's browsers. Are you a spammer? (just answer the question) Preparation code Preparation code HTML (this will be inserted in the <body> of a valid HTML5 document in standards mode) (useful when testing DOM operations or including libraries) Include JavaScript libraries as follows: <script src="//cdn.ext/library.js"></script> Define setup for all tests (variables, functions, arrays or other objects that will be used in the tests) (runs before each clocked test loop, outside of the timed code region) (e.g. define local test variables, reset global variables, clear canvas, etc.) (see FAQ) var i, l, x, arr = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"]; Define teardown for all tests (runs after each clocked test loop, outside of the timed code region) (see FAQ) Code snippets to compare Test 1 Title Async (check if this is an asynchronous test) Code for (i = 0, l = arr.length; i < l; i++) { x = arr[i]; } Test 2 Title Async (check if this is an asynchronous test) Code for (i = 0; i < arr.length; i++) { x = arr[i]; }