We can use the replacer to specify the entries to be serialized. Maps are normally serialized as objects with no properties. To transfer large numbers without loss of precision, serialize them as strings, and revive them to BigInts, or other appropriate arbitrary precision formats. So, for example, numbers in JSON text will have already been converted to JavaScript numbers, and may lose precision in the process. Note that reviver is run after the value is parsed. For JSON text parsing to primitive values, reviver will be called once. Similar to the replacer parameter of JSON.stringify(), reviver will be last called on the root object with an empty string as the key and the root object as the value. If the reviver only transforms some values and not others, be certain to return all untransformed values as-is - otherwise, they will be deleted from the resulting object. Otherwise, the property is redefined to be the return value.
If the reviver function returns undefined (or returns no value - for example, if execution falls off the end of the function), the property is deleted from the object. The reviver is called with the object containing the property being processed as this, and two arguments: key and value, representing the property name as a string (even for arrays) and the property value. Specifically, the computed value and all its properties (in a depth-first fashion, beginning with the most nested properties and proceeding to the original value itself) are individually run through the reviver. If a reviver is specified, the value computed by parsing is transformed before being returned.
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