Handle “undefined” as passed option values (#146)

Allow the consumers to pass “undefined” as options values instead of misbehaving.

Today if the consumer passes “undefined”, we ignore the default options and allow the “undefined” value to fall through to the rest of the program, resulting in undefined behavior. For an example, the maxDelta becomes NaN if threshold: undefined is provided.

After this change we ensure that “undefined” as options values is converted into a default value.

It is customary in JavaScript, especially in options objects, to treat a missing key and a key with value of undefined the same way. In particular, it is a distinction that is easily introduced when the customer receives a value from somewhere else and wants to continue to support default values.

index.js

@@ -1,15 +1,14 @@
 
-const defaultOptions = {
-    threshold: 0.1,         // matching threshold (0 to 1); smaller is more sensitive
-    includeAA: false,       // whether to skip anti-aliasing detection
-    alpha: 0.1,             // opacity of original image in diff output
-    aaColor: [255, 255, 0], // color of anti-aliased pixels in diff output
-    diffColor: [255, 0, 0], // color of different pixels in diff output
-    diffColorAlt: null,     // whether to detect dark on light differences between img1 and img2 and set an alternative color to differentiate between the two
-    diffMask: false         // draw the diff over a transparent background (a mask)
-};
-
 export default function pixelmatch(img1, img2, output, width, height, options) {
+    const {
+        threshold = 0.1,         // matching threshold (0 to 1); smaller is more sensitive
+        includeAA = false,       // whether to skip anti-aliasing detection
+        alpha = 0.1,             // opacity of original image in diff output
+        aaColor = [255, 255, 0], // color of anti-aliased pixels in diff output
+        diffColor = [255, 0, 0], // color of different pixels in diff output
+        diffColorAlt = null,     // whether to detect dark on light differences between img1 and img2 and set an alternative color to differentiate between the two
+        diffMask = false         // draw the diff over a transparent background (a mask)
+    } = options;
 
     if (!isPixelData(img1) || !isPixelData(img2) || (output && !isPixelData(output)))
         throw new Error('Image data: Uint8Array, Uint8ClampedArray or Buffer expected.');
@@ -19,8 +18,6 @@ export default function pixelmatch(img1, img2, output, width, height, options) {
 
     if (img1.length !== width * height * 4) throw new Error('Image data size does not match width/height.');
 
-    options = Object.assign({}, defaultOptions, options);
-
     // check if images are identical
     const len = width * height;
     const a32 = new Uint32Array(img1.buffer, img1.byteOffset, len);
@@ -31,18 +28,18 @@ export default function pixelmatch(img1, img2, output, width, height, options) {
         if (a32[i] !== b32[i]) { identical = false; break; }
     }
     if (identical) { // fast path if identical
-        if (output && !options.diffMask) {
-            for (let i = 0; i < len; i++) drawGrayPixel(img1, 4 * i, options.alpha, output);
+        if (output && !diffMask) {
+            for (let i = 0; i < len; i++) drawGrayPixel(img1, 4 * i, alpha, output);
         }
         return 0;
     }
 
     // maximum acceptable square distance between two colors;
     // 35215 is the maximum possible value for the YIQ difference metric
-    const maxDelta = 35215 * options.threshold * options.threshold;
-    const [aaR, aaG, aaB] = options.aaColor;
-    const [diffR, diffG, diffB] = options.diffColor;
-    const [altR, altG, altB] = options.diffColorAlt || options.diffColor;
+    const maxDelta = 35215 * threshold * threshold;
+    const [aaR, aaG, aaB] = aaColor;
+    const [diffR, diffG, diffB] = diffColor;
+    const [altR, altG, altB] = diffColorAlt || diffColor;
     let diff = 0;
 
     // compare each pixel of one image against the other one
@@ -57,11 +54,11 @@ export default function pixelmatch(img1, img2, output, width, height, options) {
             // the color difference is above the threshold
             if (Math.abs(delta) > maxDelta) {
                 // check it's a real rendering difference or just anti-aliasing
-                if (!options.includeAA && (antialiased(img1, x, y, width, height, img2) ||
+                if (!includeAA && (antialiased(img1, x, y, width, height, img2) ||
                                            antialiased(img2, x, y, width, height, img1))) {
                     // one of the pixels is anti-aliasing; draw as yellow and do not count as difference
                     // note that we do not include such pixels in a mask
-                    if (output && !options.diffMask) drawPixel(output, pos, aaR, aaG, aaB);
+                    if (output && !diffMask) drawPixel(output, pos, aaR, aaG, aaB);
 
                 } else {
                     // found substantial difference not caused by anti-aliasing; draw it as such
@@ -77,7 +74,7 @@ export default function pixelmatch(img1, img2, output, width, height, options) {
 
             } else if (output) {
                 // pixels are similar; draw background as grayscale image blended with white
-                if (!options.diffMask) drawGrayPixel(img1, pos, options.alpha, output);
+                if (!diffMask) drawGrayPixel(img1, pos, alpha, output);
             }
         }
     }

test/test.js

@@ -9,6 +9,7 @@ import match from '../index.js';
 const options = {threshold: 0.05};
 
 diffTest('1a', '1b', '1diff', options, 143);
+diffTest('1a', '1b', '1diffdefaultthreshold', {threshold: undefined}, 106);
 diffTest('1a', '1b', '1diffmask', {threshold: 0.05, includeAA: false, diffMask: true}, 143);
 diffTest('1a', '1a', '1emptydiffmask', {threshold: 0, diffMask: true}, 0);
 diffTest('2a', '2b', '2diff', {