Handle “undefined” as passed option values

[denis-sokolov]

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.

Related to #14, #52.

Alternative syntax to consider:

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;

[mourner]

Thanks! I think I'd prefer the simpler destructuring syntax — values will drop the options namespace this way but this should be OK for our purposes.

[denis-sokolov]

Updated.

[mourner]

Looks good to me! Perhaps worth adding a minimal test to validate the fix too?

[denis-sokolov]

Added a test.