Use shorter zero checks for array indices and length.

Keeping === 0 for mathematical algorithms seems clearer.

src/basic/Matrix.js

@@ -83,7 +83,7 @@ var Matrix = Base.extend(/** @lends Matrix# */{
             } else {
                 ok = false;
             }
-        } else if (count === 0) {
+        } else if (!count) {
             this.reset();
         } else {
             ok = false;

src/item/Item.js

@@ -829,7 +829,7 @@ new function() { // Injection scope for various item event handlers
         // If we're returning '#bounds', create a LinkedRectangle that uses
         // the setBounds() setter to update the Item whenever the bounds are
         // changed:
-        return arguments.length === 0
+        return !arguments.length
                 ? new LinkedRectangle(bounds.x, bounds.y, bounds.width,
                         bounds.height, this, 'setBounds')
                 : bounds;
@@ -878,7 +878,7 @@ new function() { // Injection scope for various item event handlers
         var children = this._children;
         // TODO: What to return if nothing is defined, e.g. empty Groups?
         // Scriptographer behaves weirdly then too.
-        if (!children || children.length === 0)
+        if (!children || !children.length)
             return new Rectangle();
         // Call _updateBoundsCache() even when the group only holds empty /
         // invisible items), so future changes in these items will cause right
@@ -2667,7 +2667,8 @@ new function() { // Injection scope for hit-test functions shared with project
      * @return Boolean
      */
     isEmpty: function() {
-        return !this._children || this._children.length === 0;
+        var children = this._children;
+        return !children || !children.length;
     },
 
     /**
@@ -4309,7 +4310,7 @@ new function() { // Injection scope for hit-test functions shared with project
                 // bounds corners, and draw the corners.
                 ctx.beginPath();
                 for (var i = 0; i < 8; i++) {
-                    ctx[i === 0 ? 'moveTo' : 'lineTo'](coords[i], coords[++i]);
+                    ctx[!i ? 'moveTo' : 'lineTo'](coords[i], coords[++i]);
                 }
                 ctx.closePath();
                 ctx.stroke();

src/item/Project.js

@@ -135,7 +135,7 @@ var Project = PaperScopeItem.extend(/** @lends Project# */{
      * @return Boolean
      */
     isEmpty: function() {
-        return this._children.length === 0;
+        return !this._children.length;
     },
 
     /**

src/path/CompoundPath.js

@@ -142,7 +142,7 @@ var CompoundPath = PathItem.extend(/** @lends CompoundPath# */{
             if (path.isEmpty())
                 path.remove();
         }
-        if (children.length === 0) { // Replace with a simple empty Path
+        if (!children.length) { // Replace with a simple empty Path
             var path = new Path(Item.NO_INSERT);
             path.copyAttributes(this);
             path.insertAbove(this);
@@ -301,7 +301,7 @@ var CompoundPath = PathItem.extend(/** @lends CompoundPath# */{
     _draw: function(ctx, param, viewMatrix, strokeMatrix) {
         var children = this._children;
         // Return early if the compound path doesn't have any children:
-        if (children.length === 0)
+        if (!children.length)
             return;
 
         param = param.extend({ dontStart: true, dontFinish: true });
@@ -342,7 +342,7 @@ new function() { // Injection scope for PostScript-like drawing functions
      */
     function getCurrentPath(that, check) {
         var children = that._children;
-        if (check && children.length === 0)
+        if (check && !children.length)
             throw new Error('Use a moveTo() command first');
         return children[children.length - 1];
     }

src/path/Curve.js

@@ -71,7 +71,7 @@ var Curve = Base.extend(/** @lends Curve# */{
             this._path = arg0;
             seg1 = arg1;
             seg2 = arg2;
-        } else if (count === 0) {
+        } else if (!count) {
             seg1 = new Segment();
             seg2 = new Segment();
         } else if (count === 1) {
@@ -299,7 +299,7 @@ var Curve = Base.extend(/** @lends Curve# */{
      * @return {Boolean} {@true if this is the first curve}
      */
     isFirst: function() {
-        return this._segment1._index === 0;
+        return !this._segment1._index;
     },
 
     /**
@@ -651,7 +651,7 @@ statics: /** @lends Curve */{
                 tMax = 1 - tMin,
                 roots = [],
                 n = Numerical.solveQuadratic(a, b, c, roots, tMin, tMax);
-            if (n === 0) {
+            if (!n) {
                 curves.push(v);
             } else {
                 roots.sort();
@@ -2110,13 +2110,13 @@ new function() { // Scope for intersection using bezier fat-line clipping
                 if (t2 != null) {  // If point is on curve
                     var pair = i === 0 ? [t1, t2] : [t2, t1];
                     // Filter out tiny overlaps.
-                    if (pairs.length === 0 ||
+                    if (!pairs.length ||
                         abs(pair[0] - pairs[0][0]) > timeEpsilon &&
                         abs(pair[1] - pairs[0][1]) > timeEpsilon)
                         pairs.push(pair);
                 }
                 // We checked 3 points but found no match, curves can't overlap.
-                if (i === 1 && pairs.length === 0)
+                if (i === 1 && !pairs.length)
                     break;
             }
             if (pairs.length !== 2) {

src/path/Path.js

@@ -346,7 +346,7 @@ var Path = PathItem.extend(/** @lends Path# */{
             outY = coords[5];
         }
 
-        if (length === 0)
+        if (!length)
             return '';
 
         for (var i = 0; i < length; i++)
@@ -364,7 +364,7 @@ var Path = PathItem.extend(/** @lends Path# */{
     // taken into account.
 
     isEmpty: function() {
-        return this._segments.length === 0;
+        return !this._segments.length;
     },
 
     _transformContent: function(matrix) {
@@ -457,7 +457,7 @@ var Path = PathItem.extend(/** @lends Path# */{
         }
         // If it's the first segment, correct the last segment of closed
         // paths too:
-        if (curve = curves[this._closed && start === 0 ? segments.length - 1
+        if (curve = curves[this._closed && !start ? segments.length - 1
                 : start - 1]) {
             curve._segment2 = segments[start] || segments[0];
             curve._changed();
@@ -2303,7 +2303,7 @@ new function() { // PostScript-style drawing commands
      */
     function getCurrentSegment(that) {
         var segments = that._segments;
-        if (segments.length === 0)
+        if (!segments.length)
             throw new Error('Use a moveTo() command first');
         return segments[segments.length - 1];
     }
@@ -2522,7 +2522,7 @@ new function() { // PostScript-style drawing commands
                         pt = center.add(vector);
                     }
                 }
-                if (i === 0) {
+                if (!i) {
                     // Modify startSegment
                     current.setHandleOut(out);
                 } else {
@@ -2864,7 +2864,7 @@ statics: {
             segment._transformCoordinates(matrix, coords);
             for (var j = 0; j < 6; j += 2) {
                 // Use different padding for points or handles
-                var padding = j === 0 ? joinPadding : strokePadding,
+                var padding = !j ? joinPadding : strokePadding,
                     paddingX = padding ? padding[0] : 0,
                     paddingY = padding ? padding[1] : 0,
                     x = coords[j],

src/path/PathItem.Boolean.js

@@ -482,7 +482,7 @@ PathItem.inject(new function() {
             var curve = curves[i],
                 path = curve._path,
                 v = curve.getValues();
-            if (i === 0 || curves[i - 1]._path !== path) {
+            if (!i || curves[i - 1]._path !== path) {
                 // We're on a new (sub-)path, so we need to determine values of
                 // the last non-horizontal curve on this path.
                 vPrev = null;

src/path/PathItem.js

@@ -169,7 +169,7 @@ var PathItem = Item.extend(/** @lends PathItem# */{
             case 'l':
                 var move = lower === 'm';
                 for (var j = 0; j < length; j += 2)
-                    this[j === 0 && move ? 'moveTo' : 'lineTo'](
+                    this[!j && move ? 'moveTo' : 'lineTo'](
                             current = getPoint(j));
                 control = current;
                 if (move)

src/path/PathIterator.js

@@ -110,7 +110,7 @@ var PathIterator = Base.extend({
         var i, j = this.index;
         for (;;) {
             i = j;
-            if (j === 0 || this.parts[--j].offset < offset)
+            if (!j || this.parts[--j].offset < offset)
                 break;
         }
         // Find the part that succeeds the given offset, then interpolate

src/path/Segment.js

@@ -496,7 +496,7 @@ var Segment = Base.extend(/** @lends Segment# */{
      * @return {Boolean} {@true if this is the first segment}
      */
     isFirst: function() {
-        return this._index === 0;
+        return !this._index;
     },
 
     /**

src/style/Color.js

@@ -588,7 +588,7 @@ var Color = Base.extend(new function() {
                             // Allow implicit definition of gradients through
                             // stops / radial properties. Conversion happens
                             // here on the fly:
-                            if (value == null && i === 0 && type === 'gradient'
+                            if (value == null && !i && type === 'gradient'
                                     && 'stops' in arg) {
                                 value = {
                                     stops: arg.stops,

src/style/Gradient.js

@@ -119,7 +119,7 @@ var Gradient = Base.extend(/** @lends Gradient# */{
         var index = this._owners ? this._owners.indexOf(color) : -1;
         if (index != -1) {
             this._owners.splice(index, 1);
-            if (this._owners.length === 0)
+            if (!this._owners.length)
                 this._owners = undefined;
         }
     },

src/style/Style.js

@@ -203,7 +203,7 @@ var Style = Base.extend(new function() {
             // If the owner has children, walk through all of them and see if
             // they all have the same style.
             // If true is passed for _dontMerge, don't merge children styles
-            if (key in this._defaults && (!children || children.length === 0
+            if (key in this._defaults && (!children || !children.length
                     || _dontMerge || owner instanceof CompoundPath)) {
                 var value = this._values[key];
                 if (value === undefined) {
@@ -224,7 +224,7 @@ var Style = Base.extend(new function() {
             } else if (children) {
                 for (var i = 0, l = children.length; i < l; i++) {
                     var childValue = children[i]._style[get]();
-                    if (i === 0) {
+                    if (!i) {
                         value = childValue;
                     } else if (!Base.equals(value, childValue)) {
                         // If there is another child with a different

test/tests/CompoundPath.js

@@ -23,7 +23,7 @@ test('moveTo() / lineTo()', function() {
     for (var i = 0; i < lists.length; i++) {
         var list = lists[i];
         for (var j = 0; j < list.length; j++) {
-            path[j === 0 ? 'moveTo' : 'lineTo'](list[j]);
+            path[!j ? 'moveTo' : 'lineTo'](list[j]);
         }
     }