Function addObjectEntriesMutate

Adds an object to an existing map, mutating it. It assumes a structure where each top-level property is a key:

const data = {
 Sally: { colour: `red` },
 Bob:   { colour: `pink` }
};
const map = new Map();
addObjectEntriesMutate(map, data);

map.get(`Sally`); // { name: `Sally`, colour: `red` }
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To create a new map from an object, use fromObject instead.