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Replace PointerMap with potentially-sparse-array-based Map polyfill #190

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Replace PointerMap with potentially-sparse-array-based Map polyfill #190

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60 changes: 26 additions & 34 deletions src/pointermap.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2,55 +2,47 @@
* This module implements an map of pointer states
*/
var USE_MAP = window.Map && window.Map.prototype.forEach;
var POINTERS_FN = function() { return this.size; };
function PointerMap() {
if (USE_MAP) {
var m = new Map();
m.pointers = POINTERS_FN;
return m;
} else {
this.keys = [];
this.values = [];
}
return USE_MAP ? new Map() : new SparseArrayMap();
}

function SparseArrayMap() {
this.array = [];
this.size = 0;
}

PointerMap.prototype = {
set: function(inId, inEvent) {
var i = this.keys.indexOf(inId);
if (i > -1) {
this.values[i] = inEvent;
} else {
this.keys.push(inId);
this.values.push(inEvent);
SparseArrayMap.prototype = {
set: function(k, v) {
if (v === undefined) {
return this.delete(k);
}
if (!this.has(k)) {
this.size++;
}
this.array[k] = v;
},
has: function(inId) {
return this.keys.indexOf(inId) > -1;
has: function(k) {
return this.array[k] !== undefined;
},
delete: function(inId) {
var i = this.keys.indexOf(inId);
if (i > -1) {
this.keys.splice(i, 1);
this.values.splice(i, 1);
delete: function(k) {
if (this.has(k)) {
delete this.array[k];
this.size--;
}
},
get: function(inId) {
var i = this.keys.indexOf(inId);
return this.values[i];
get: function(k) {
return this.array[k];
},
clear: function() {
this.keys.length = 0;
this.values.length = 0;
this.array.length = 0;
this.size = 0;
},

// return value, key, map
forEach: function(callback, thisArg) {
this.values.forEach(function(v, i) {
callback.call(thisArg, v, this.keys[i], this);
return this.array.forEach(function(v, k) {
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Why is this returning?

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Tail position.

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Do you care to explain in plain English instead of spec prose?

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Ending a function in tail position allows for tail call optimization - basically, functions that end with "return" and a call to another function relinquish their stack space to the next function.

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As far as I know no JS engine currently supports that optimization.

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No engine supports that optimization yet, but it's slated, so why not be ready for it?

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so why not be ready for it?

It may avoid call stack limits but there's no guarantee it'll bring a perf win. It's probably better to program for things that are a bit more tangible.

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Is there any chance that there will be support of tail recursion in browsers, which don't support native Map? Or am I missing something?

callback.call(thisArg, v, k, this);
}, this);
},
pointers: function() {
return this.keys.length;
}
};

Expand Down
6 changes: 3 additions & 3 deletions src/touch.js
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Original file line number Diff line number Diff line change
Expand Up @@ -112,7 +112,7 @@ var touchEvents = {
setPrimaryTouch: function(inTouch) {

// set primary touch if there no pointers, or the only pointer is the mouse
if (pointermap.pointers() === 0 || (pointermap.pointers() === 1 && pointermap.has(1))) {
if (pointermap.size === 0 || (pointermap.size === 1 && pointermap.has(1))) {
this.firstTouch = inTouch.identifier;
this.firstXY = { X: inTouch.clientX, Y: inTouch.clientY };
this.scrolling = false;
Expand Down Expand Up @@ -233,9 +233,9 @@ var touchEvents = {
vacuumTouches: function(inEvent) {
var tl = inEvent.touches;

// pointermap.pointers() should be < tl.length here, as the touchstart has not
// pointermap.size should be < tl.length here, as the touchstart has not
// been processed yet.
if (pointermap.pointers() >= tl.length) {
if (pointermap.size >= tl.length) {
var d = [];
pointermap.forEach(function(value, key) {

Expand Down
24 changes: 10 additions & 14 deletions tests/unit/pointermap.js
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,7 @@ define([
'get',
'has',
'delete',
'pointers',
'size',
'clear',
'forEach'
];
Expand All @@ -26,20 +26,16 @@ define([
test('PointerMap .set', function() {
var p = new PointerMap();
p.set(1, true);
if (!window.Map || !(p instanceof Map)) {
expect(p.keys).to.have.length(1);
expect(p.values).to.have.length(1);
}
expect(p.pointers()).to.equal(1);
expect(p.size).to.equal(1);
});
test('PointerMap .pointers', function() {
test('PointerMap .size', function() {
var p = new PointerMap();
expect(p.pointers).to.be.a('function');
expect(p.pointers()).to.equal(0);
expect(p.size).to.be.a('number');
expect(p.size).to.equal(0);
p.set(1, true);
expect(p.pointers()).to.equal(1);
expect(p.size).to.equal(1);
p.set(1, false);
expect(p.pointers()).to.equal(1);
expect(p.size).to.equal(1);
});
test('PointerMap .has', function() {
var p = new PointerMap();
Expand All @@ -51,16 +47,16 @@ define([
var p = new PointerMap();
p.set(1, true);
p.set(2, false);
expect(p.pointers()).to.equal(2);
expect(p.size).to.equal(2);
p.delete(1);
expect(p.pointers()).to.equal(1);
expect(p.size).to.equal(1);
expect(p.get(2)).to.equal(false);
});
test('PointerMap .clear', function() {
var p = new PointerMap();
p.set(1, true);
p.clear();
expect(p.pointers()).to.equal(0);
expect(p.size).to.equal(0);
});
test('PointerMap .forEach', function() {
var p = new PointerMap();
Expand Down