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Implement relative scroll time from distance #167

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Implement relative scroll time from distance #167

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18d5182
Implement relative scroll time from distance
luispuig Nov 26, 2020
6d8e7e2
Improve code explinations
luispuig Nov 30, 2020
26c52db
Move SCROLL_SPEED to globals
luispuig Nov 30, 2020
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22 changes: 15 additions & 7 deletions src/smoothscroll.js
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Original file line number Diff line number Diff line change
Expand Up @@ -16,7 +16,8 @@ function polyfill() {

// globals
var Element = w.HTMLElement || w.Element;
var SCROLL_TIME = 468;
var MIN_SCROLL_TIME = 200;
var MAX_SCROLL_TIME = 468;

// object gathering original scroll methods
var original = {
Expand Down Expand Up @@ -174,7 +175,7 @@ function polyfill() {
var value;
var currentX;
var currentY;
var elapsed = (time - context.startTime) / SCROLL_TIME;
var elapsed = (time - context.startTime) / context.scrollTime;

// avoid elapsed times higher than one
elapsed = elapsed > 1 ? 1 : elapsed;
Expand Down Expand Up @@ -221,6 +222,12 @@ function polyfill() {
method = scrollElement;
}

const maxDistance = Math.max(Math.abs(x - startX), Math.abs(y - startY));

@jeremenichelli jeremenichelli Nov 29, 2020

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Can we add a comment on top of this two lines of math operations (not that is unclear what they do), it will help people reading the code for the first time a lot, to understand the reasoning and why we are doing it.

@luispuig luispuig Nov 30, 2020

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Sure, let put it in 2 lines and better for others to modify it in the future.

@luispuig luispuig Nov 30, 2020

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Please, feel free to suggest a different explanation, comments, etc...
Also, I added the animation speed which is 1 pixel/ms. It will make it easier to modify it you think that another value matches better the native bahaivour.

const scrollTime = Math.max(
MIN_SCROLL_TIME,
Math.min(MAX_SCROLL_TIME, maxDistance)
);

// scroll looping over a frame
step({
scrollable: scrollable,
Expand All @@ -229,7 +236,8 @@ function polyfill() {
startX: startX,
startY: startY,
x: x,
y: y
y: y,
scrollTime
});
}

Expand All @@ -248,14 +256,14 @@ function polyfill() {
arguments[0].left !== undefined
? arguments[0].left
: typeof arguments[0] !== 'object'
? arguments[0]
: w.scrollX || w.pageXOffset,
? arguments[0]
: w.scrollX || w.pageXOffset,
// use top prop, second argument if present or fallback to scrollY
arguments[0].top !== undefined
? arguments[0].top
: arguments[1] !== undefined
? arguments[1]
: w.scrollY || w.pageYOffset
? arguments[1]
: w.scrollY || w.pageYOffset
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);

return;
Expand Down