I’m not sure about more efficient in terms of big-O but certainly using the unshift method is more concise: var a = [1, 2, 3, 4]; a.unshift(0); // => [0, 1, 2, 3, 4] console.log({a}); [Edit] This jsPerf benchmark shows that unshift is decently faster in at least a couple of browsers, regardless of possibly … Read more
Store a reference to the first message before you prepend new messages, and after you prepend, set the scroll to the offset of that message: $(document).on(‘scroll’, function() { var scroll = $(document).scrollTop(); if (scroll < 1) { // Store eference to first message var firstMsg = $(‘.message:first’); // Prepend new message here (I’m just cloning…) … Read more
>>> x = 42 >>> xs = [1, 2, 3] >>> xs.insert(0, x) >>> xs [42, 1, 2, 3] How it works: list.insert(index, value) Insert an item at a given position. The first argument is the index of the element before which to insert, so xs.insert(0, x) inserts at the front of the list, and … Read more
See: .append() puts data inside an element at last index and .prepend() puts the prepending elem at first index suppose: <div class=”a”> //<—you want div c to append in this <div class=”b”>b</div> </div> when .append() executes it will look like this: $(‘.a’).append($(‘.c’)); after execution: <div class=”a”> //<—you want div c to append in this <div … Read more
The s.insert(0, x) form is the most common. Whenever you see it though, it may be time to consider using a collections.deque instead of a list. Prepending to a deque runs in constant time. Prepending to a list runs in linear time.
printf ‘%s\n%s\n’ “to be prepended” “$(cat text.txt)” >text.txt
If someFunction is globally available, then you can cache the function, create your own, and have yours call it. So if this is the original… someFunction = function() { alert(“done”); } You’d do this… someFunction = (function() { var cached_function = someFunction; return function() { // your code var result = cached_function.apply(this, arguments); // use … Read more
Here’s a snippet to get you going: theParent = document.getElementById(“theParent”); theKid = document.createElement(“div”); theKid.innerHTML = ‘Are we there yet?’; // append theKid to the end of theParent theParent.appendChild(theKid); // prepend theKid to the beginning of theParent theParent.insertBefore(theKid, theParent.firstChild); theParent.firstChild will give us a reference to the first element within theParent and put theKid before it.
Python makes a lot of things easy and contains libraries and wrappers for a lot of common operations, but the goal is not to hide fundamental truths. The fundamental truth you are encountering here is that you generally can’t prepend data to an existing flat structure without rewriting the entire structure. This is true regardless … Read more