Function mapObjectShallow

Maps the top-level properties of an object through a map function. That is, run each of the values of an object through a function, setting the result onto the same key structure as original.

It is NOT recursive.

The mapping function gets a single args object, consisting of { value, field, index }, where 'value' is the value of the field, 'field' the name, and 'index' a numeric count.

Example: Double the value of all fields

const rect = { width: 100, height: 250 };
const doubled = mapObjectShallow(rect, args => {
 return args.value*2;
});
// Yields: { width: 200, height: 500 }
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Since the map callback gets the name of the property, it can do context-dependent things.

const rect = { width: 100, height: 250, colour: 'red' }
const doubled = mapObjectShallow(rect, args => {
 if (args.field === 'width') return args.value*3;
 else if (typeof args.value === 'number') return args.value*2;
 return args.value;
});
// Yields: { width: 300, height: 500, colour: 'red' }
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In addition to bulk processing, it allows remapping of property types.

In terms of type-safety, the mapped properties are assumed to have the same type.

const o = {
 x: 10,
 y: 20,
 width: 200,
 height: 200
}

// Make each property use an averager instead
const oAvg = mapObjectShallow(o, args => {
 return movingAverage(10);
});

// Instead of { x:number, y:number... }, we now have { x:movingAverage(), y:movingAverage()... }
// Add a value to the averager
oAvg.x.add(20);
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