diff --git a/.npmignore b/.npmignore
index d4a3e9b..6fb58a1 100644
--- a/.npmignore
+++ b/.npmignore
@@ -5,4 +5,5 @@ node_modules
 src
 tslint.json
 rollup.config.js
-.gitignore
\ No newline at end of file
+.gitignore
+visual-tests
\ No newline at end of file
diff --git a/src/fillers/dashed-filler.ts b/src/fillers/dashed-filler.ts
index 3a03c43..2b24642 100644
--- a/src/fillers/dashed-filler.ts
+++ b/src/fillers/dashed-filler.ts
@@ -18,7 +18,7 @@ export class DashedFiller implements PatternFiller {
   private dashedLine(lines: Line[], o: ResolvedOptions): Op[] {
     const offset = o.dashOffset < 0 ? (o.hachureGap < 0 ? (o.strokeWidth * 4) : o.hachureGap) : o.dashOffset;
     const gap = o.dashGap < 0 ? (o.hachureGap < 0 ? (o.strokeWidth * 4) : o.hachureGap) : o.dashGap;
-    let ops: Op[] = [];
+    const ops: Op[] = [];
     lines.forEach((line) => {
       const length = lineLength(line);
       const count = Math.floor(length / (offset + gap));
@@ -35,7 +35,7 @@ export class DashedFiller implements PatternFiller {
         const lend = lstart + offset;
         const start: Point = [p1[0] + (lstart * Math.cos(alpha)) + (startOffset * Math.cos(alpha)), p1[1] + lstart * Math.sin(alpha) + (startOffset * Math.sin(alpha))];
         const end: Point = [p1[0] + (lend * Math.cos(alpha)) + (startOffset * Math.cos(alpha)), p1[1] + (lend * Math.sin(alpha)) + (startOffset * Math.sin(alpha))];
-        ops = ops.concat(this.helper.doubleLineOps(start[0], start[1], end[0], end[1], o));
+        ops.push(...this.helper.doubleLineOps(start[0], start[1], end[0], end[1], o));
       }
     });
     return ops;
diff --git a/src/fillers/dot-filler.ts b/src/fillers/dot-filler.ts
index 12b5f19..9818b5d 100644
--- a/src/fillers/dot-filler.ts
+++ b/src/fillers/dot-filler.ts
@@ -17,7 +17,7 @@ export class DotFiller implements PatternFiller {
   }
 
   private dotsOnLines(lines: Line[], o: ResolvedOptions): OpSet {
-    let ops: Op[] = [];
+    const ops: Op[] = [];
     let gap = o.hachureGap;
     if (gap < 0) {
       gap = o.strokeWidth * 4;
@@ -40,7 +40,7 @@ export class DotFiller implements PatternFiller {
         const cx = this.helper.randOffsetWithRange(c[0] - gap / 4, c[0] + gap / 4, o);
         const cy = this.helper.randOffsetWithRange(c[1] - gap / 4, c[1] + gap / 4, o);
         const el = this.helper.ellipse(cx, cy, fweight, fweight, o);
-        ops = ops.concat(el.ops);
+        ops.push(...el.ops);
       }
     }
     return { type: 'fillSketch', ops };
diff --git a/src/fillers/hachure-filler.ts b/src/fillers/hachure-filler.ts
index de9b71e..4ec9249 100644
--- a/src/fillers/hachure-filler.ts
+++ b/src/fillers/hachure-filler.ts
@@ -21,12 +21,12 @@ export class HachureFiller implements PatternFiller {
   }
 
   private renderLines(lines: Line[], o: ResolvedOptions, connectEnds: boolean): Op[] {
-    let ops: Op[] = [];
+    const ops: Op[] = [];
     let prevPoint: Point | null = null;
     for (const line of lines) {
-      ops = ops.concat(this.helper.doubleLineOps(line[0][0], line[0][1], line[1][0], line[1][1], o));
+      ops.push(...this.helper.doubleLineOps(line[0][0], line[0][1], line[1][0], line[1][1], o));
       if (connectEnds && prevPoint) {
-        ops = ops.concat(this.helper.doubleLineOps(prevPoint[0], prevPoint[1], line[0][0], line[0][1], o));
+        ops.push(...this.helper.doubleLineOps(prevPoint[0], prevPoint[1], line[0][0], line[0][1], o));
       }
       prevPoint = line[1];
     }
diff --git a/src/fillers/zigzag-line-filler.ts b/src/fillers/zigzag-line-filler.ts
index ccb3833..177f205 100644
--- a/src/fillers/zigzag-line-filler.ts
+++ b/src/fillers/zigzag-line-filler.ts
@@ -19,7 +19,7 @@ export class ZigZagLineFiller implements PatternFiller {
   }
 
   private zigzagLines(lines: Line[], zo: number, o: ResolvedOptions): Op[] {
-    let ops: Op[] = [];
+    const ops: Op[] = [];
     lines.forEach((line) => {
       const length = lineLength(line);
       const count = Math.round(length / (2 * zo));
@@ -37,8 +37,10 @@ export class ZigZagLineFiller implements PatternFiller {
         const start: Point = [p1[0] + (lstart * Math.cos(alpha)), p1[1] + lstart * Math.sin(alpha)];
         const end: Point = [p1[0] + (lend * Math.cos(alpha)), p1[1] + (lend * Math.sin(alpha))];
         const middle: Point = [start[0] + dz * Math.cos(alpha + Math.PI / 4), start[1] + dz * Math.sin(alpha + Math.PI / 4)];
-        ops = ops.concat(this.helper.doubleLineOps(start[0], start[1], middle[0], middle[1], o));
-        ops = ops.concat(this.helper.doubleLineOps(middle[0], middle[1], end[0], end[1], o));
+        ops.push(
+          ...this.helper.doubleLineOps(start[0], start[1], middle[0], middle[1], o),
+          ...this.helper.doubleLineOps(middle[0], middle[1], end[0], end[1], o)
+        );
       }
     });
     return ops;
diff --git a/src/renderer.ts b/src/renderer.ts
index 6a79346..fd548dc 100644
--- a/src/renderer.ts
+++ b/src/renderer.ts
@@ -25,12 +25,12 @@ export function line(x1: number, y1: number, x2: number, y2: number, o: Resolved
 export function linearPath(points: Point[], close: boolean, o: ResolvedOptions): OpSet {
   const len = (points || []).length;
   if (len > 2) {
-    let ops: Op[] = [];
+    const ops: Op[] = [];
     for (let i = 0; i < (len - 1); i++) {
-      ops = ops.concat(_doubleLine(points[i][0], points[i][1], points[i + 1][0], points[i + 1][1], o));
+      ops.push(..._doubleLine(points[i][0], points[i][1], points[i + 1][0], points[i + 1][1], o));
     }
     if (close) {
-      ops = ops.concat(_doubleLine(points[len - 1][0], points[len - 1][1], points[0][0], points[0][1], o));
+      ops.push(..._doubleLine(points[len - 1][0], points[len - 1][1], points[0][0], points[0][1], o));
     }
     return { type: 'path', ops };
   } else if (len === 2) {
@@ -45,7 +45,10 @@ export function polygon(points: Point[], o: ResolvedOptions): OpSet {
 
 export function rectangle(x: number, y: number, width: number, height: number, o: ResolvedOptions): OpSet {
   const points: Point[] = [
-    [x, y], [x + width, y], [x + width, y + height], [x, y + height]
+    [x, y],
+    [x + width, y],
+    [x + width, y + height],
+    [x, y + height]
   ];
   return polygon(points, o);
 }
@@ -110,14 +113,18 @@ export function arc(x: number, y: number, width: number, height: number, start:
   const arcInc = Math.min(ellipseInc / 2, (stp - strt) / 2);
   const o1 = _arc(arcInc, cx, cy, rx, ry, strt, stp, 1, o);
   const o2 = _arc(arcInc, cx, cy, rx, ry, strt, stp, 1.5, o);
-  let ops = o1.concat(o2);
+  const ops = o1.concat(o2);
   if (closed) {
     if (roughClosure) {
-      ops = ops.concat(_doubleLine(cx, cy, cx + rx * Math.cos(strt), cy + ry * Math.sin(strt), o));
-      ops = ops.concat(_doubleLine(cx, cy, cx + rx * Math.cos(stp), cy + ry * Math.sin(stp), o));
+      ops.push(
+        ..._doubleLine(cx, cy, cx + rx * Math.cos(strt), cy + ry * Math.sin(strt), o),
+        ..._doubleLine(cx, cy, cx + rx * Math.cos(stp), cy + ry * Math.sin(stp), o)
+      );
     } else {
-      ops.push({ op: 'lineTo', data: [cx, cy] });
-      ops.push({ op: 'lineTo', data: [cx + rx * Math.cos(strt), cy + ry * Math.sin(strt)] });
+      ops.push(
+        { op: 'lineTo', data: [cx, cy] },
+        { op: 'lineTo', data: [cx + rx * Math.cos(strt), cy + ry * Math.sin(strt)] }
+      );
     }
   }
   return { type: 'path', ops };
@@ -334,7 +341,7 @@ function _curveWithOffset(points: Point[], offset: number, o: ResolvedOptions):
 
 function _curve(points: Point[], closePoint: Point | null, o: ResolvedOptions): Op[] {
   const len = points.length;
-  let ops: Op[] = [];
+  const ops: Op[] = [];
   if (len > 3) {
     const b = [];
     const s = 1 - o.curveTightness;
@@ -360,7 +367,7 @@ function _curve(points: Point[], closePoint: Point | null, o: ResolvedOptions):
         points[2][0], points[2][1]]
     });
   } else if (len === 2) {
-    ops = ops.concat(_doubleLine(points[0][0], points[0][1], points[1][0], points[1][1], o));
+    ops.push(..._doubleLine(points[0][0], points[0][1], points[1][0], points[1][1], o));
   }
   return ops;
 }
diff --git a/visual-tests/canvas/line.html b/visual-tests/canvas/line.html
new file mode 100644
index 0000000..e69de29