Indeed, they don't support this variant, MDN articles should be updated.
One way to polyfill this method is to run the scroll method in a requestAnimationFrame powered loop. Nothing too fancy here.
The main problem that arises is how to detect when this variant is not supported. actually @nlawson's answer tackles this problem perfectly...
For this, we can use the fact that a call to Window#scroll will fire a ScrollEvent if the viewPort actually did scroll.
This means we can set up an asynchronous test that will:
- Attach an event handler to the ScrollEvent,
- Call a first time
scroll(left , top) variant to be sure the Event will fire,
- Overwrite this call with a second one using the options variant.
- In the event handler, if we aren't at the correct scroll position, this means we need to attach our polyfill.
So the caveat of this test is that it is an asynchronous test. But since you need to actually wait for the document has loaded before calling this method, I guess in 99% of cases it will be ok.
Now to less burden the main doc, and since it is already an asynchronous test, we can even wrap this test inside an iframe, which gives us something like:
/* Polyfills the Window#scroll(options) & Window#scrollTo(options) */
(function ScrollPolyfill() {
// The asynchronous tester
// wrapped in an iframe (will not work in SO's StackSnippet®)
var iframe = document.createElement('iframe');
iframe.onload = function() {
var win = iframe.contentWindow;
// listen for a scroll event
win.addEventListener('scroll', function handler(e){
// when the scroll event fires, check that we did move
if(win.pageXOffset < 99) { // !== 0 should be enough, but better be safe
attachPolyfill();
}
// cleanup
document.body.removeChild(iframe);
});
// set up our document so we can scroll
var body = win.document.body;
body.style.width = body.style.height = '1000px';
win.scrollTo(10, 0); // force the event
win.scrollTo({left:100, behavior:'instant'}); // the one we actually test
};
// prepare our frame
iframe.src = "about:blank";
iframe.setAttribute('width', 1);
iframe.setAttribute('height', 1);
iframe.setAttribute('style', 'position:absolute;z-index:-1');
iframe.onerror = function() {
console.error('failed to load the frame, try in jsfiddle');
};
document.body.appendChild(iframe);
// The Polyfill
function attachPolyfill() {
var original = window.scroll, // keep the original method around
animating = false, // will keep our timer's id
dx = 0,
dy = 0,
target = null;
// override our methods
window.scrollTo = window.scroll = function polyfilledScroll(user_opts) {
// if we are already smooth scrolling, we need to stop the previous one
// whatever the current arguments are
if(animating) {
clearAnimationFrame(animating);
}
// not the object syntax, use the default
if(arguments.length === 2) {
return original.apply(this, arguments);
}
if(!user_opts || typeof user_opts !== 'object') {
throw new TypeError("value can't be converted to a dictionnary");
}
// create a clone to not mess the passed object
// and set missing entries
var opts = {
left: ('left' in user_opts) ? user_opts.left : window.pageXOffset,
top: ('top' in user_opts) ? user_opts.top : window.pageYOffset,
behavior: ('behavior' in user_opts) ? user_opts.behavior : 'auto',
};
if(opts.behavior !== 'instant' && opts.behavior !== 'smooth') {
// parse 'auto' based on CSS computed value of 'smooth-behavior' property
// But note that if the browser doesn't support this variant
// There are good chances it doesn't support the CSS property either...
opts.behavior = window.getComputedStyle(document.scrollingElement || document.body)
.getPropertyValue('scroll-behavior') === 'smooth' ?
'smooth' : 'instant';
}
if(opts.behavior === 'instant') {
// not smooth, just default to the original after parsing the oject
return original.call(this, opts.left, opts.top);
}
// update our direction
dx = (opts.left - window.pageXOffset) || 0;
dy = (opts.top - window.pageYOffset) || 0;
// going nowhere
if(!dx && !dy) {
return;
}
// save passed arguments
target = opts;
// save the rAF id
animating = anim();
};
// the animation loop
function anim() {
var freq = 16 / 300, // whole anim duration is approximately 300ms @60fps
posX, poxY;
if( // we already reached our goal on this axis ?
(dx <= 0 && window.pageXOffset <= +target.left) ||
(dx >= 0 && window.pageXOffset >= +target.left)
){
posX = +target.left;
}
else {
posX = window.pageXOffset + (dx * freq);
}
if(
(dy <= 0 && window.pageYOffset <= +target.top) ||
(dy >= 0 && window.pageYOffset >= +target.top)
){
posY = +target.top;
}
else {
posY = window.pageYOffset + (dx * freq);
}
// move to the new position
original.call(window, posX, posY);
// while we are not ok on both axis
if(posX !== +target.left || posY !== +target.top) {
requestAnimationFrame(anim);
}
else {
animating = false;
}
}
}
})();
Sorry for not providing a runable demo inside the answer directly, but StackSnippet®'s over-protected iframes don't allow us to access the content of an inner iframe on IE...
So instead, here is a link to a jsfiddle.
Post-scriptum:
Now comes to my mind that it might actually be possible to check for support in a synchronous way by checking for the CSS scroll-behavior support, but I'm not sure it really covers all UAs in the history...
Post-Post-scriptum:
Using @nlawson's detection we can now have a working snippet ;-)
/* Polyfills the Window#scroll(options) & Window#scrollTo(options) */
(function ScrollPolyfill() {
// The synchronous tester from @nlawson's answer
var supports = false
test_el = document.createElement('div'),
test_opts = {top:0};
// ES5 style for IE
Object.defineProperty(test_opts, 'behavior', {
get: function() {
supports = true;
}
});
try {
test_el.scrollTo(test_opts);
}catch(e){};
if(!supports) {
attachPolyfill();
}
function attachPolyfill() {
var original = window.scroll, // keep the original method around
animating = false, // will keep our timer's id
dx = 0,
dy = 0,
target = null;
// override our methods
window.scrollTo = window.scroll = function polyfilledScroll(user_opts) {
// if we are already smooth scrolling, we need to stop the previous one
// whatever the current arguments are
if(animating) {
clearAnimationFrame(animating);
}
// not the object syntax, use the default
if(arguments.length === 2) {
return original.apply(this, arguments);
}
if(!user_opts || typeof user_opts !== 'object') {
throw new TypeError("value can't be converted to a dictionnary");
}
// create a clone to not mess the passed object
// and set missing entries
var opts = {
left: ('left' in user_opts) ? user_opts.left : window.pageXOffset,
top: ('top' in user_opts) ? user_opts.top : window.pageYOffset,
behavior: ('behavior' in user_opts) ? user_opts.behavior : 'auto',
};
if(opts.behavior !== 'instant' && opts.behavior !== 'smooth') {
// parse 'auto' based on CSS computed value of 'smooth-behavior' property
// But note that if the browser doesn't support this variant
// There are good chances it doesn't support the CSS property either...
opts.behavior = window.getComputedStyle(document.scrollingElement || document.body)
.getPropertyValue('scroll-behavior') === 'smooth' ?
'smooth' : 'instant';
}
if(opts.behavior === 'instant') {
// not smooth, just default to the original after parsing the oject
return original.call(this, opts.left, opts.top);
}
// update our direction
dx = (opts.left - window.pageXOffset) || 0;
dy = (opts.top - window.pageYOffset) || 0;
// going nowhere
if(!dx && !dy) {
return;
}
// save passed arguments
target = opts;
// save the rAF id
animating = anim();
};
// the animation loop
function anim() {
var freq = 16 / 300, // whole anim duration is approximately 300ms @60fps
posX, poxY;
if( // we already reached our goal on this axis ?
(dx <= 0 && window.pageXOffset <= +target.left) ||
(dx >= 0 && window.pageXOffset >= +target.left)
){
posX = +target.left;
}
else {
posX = window.pageXOffset + (dx * freq);
}
if(
(dy <= 0 && window.pageYOffset <= +target.top) ||
(dy >= 0 && window.pageYOffset >= +target.top)
){
posY = +target.top;
}
else {
posY = window.pageYOffset + (dx * freq);
}
// move to the new position
original.call(window, posX, posY);
// while we are not ok on both axis
if(posX !== +target.left || posY !== +target.top) {
requestAnimationFrame(anim);
}
else {
animating = false;
}
}
}
})();
// OP's code,
// by the time you click the button, the polyfill should already be set up if needed
function scrollWin() {
window.scrollTo({
left: 1000,
top: 1000,
behavior: 'smooth'
});
}
body {
height: 5000px;
width: 5000px;
}
<p>Click the button to scroll the document window to 1000 pixels.</p>
<button onclick="scrollWin()">Click me to scroll!</button>
