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// @flow
// Deep freeze an object by using a Proxy.
// This is better than Object.freeze() as we can create coherent error messages
// and easily only deliver frozen subobjects when they are accessed. We can
// even add custom logic, like warning if you access a property that doesn't exist.
/* eslint-disable no-console */
export default function deepFreeze<T: { [key: string]: any }>(
inputObj: T,
options: { get: boolean, set: boolean } = { get: true, set: true }
): $ReadOnly<{| ...T |}> {
// Our handler that rejects any change to the object and any nested objects inside it
const deepFreezer = {};
if (options.get) {
deepFreezer.get = function get(
obj: T,
prop: $Keys<T>,
_receiver: Proxy<T>
): any {
// Clone w/o Proxy
if (prop === "toJSON") return () => obj;
// If dealing with nested object, nest the proxy untill it reaches the direct property of it's parent proxy
if (typeof obj[prop] === "object" && obj[prop] !== null) {
return new Proxy(obj[prop], deepFreezer);
}
// If prop is directly accessible, just do the default operation
else {
if (
!(prop in obj) &&
prop !== "length" &&
prop !== "__esModule" &&
typeof prop !== "symbol"
) {
throw new Error(
`Can not get unknown prop "${String(prop)}" on frozen object.`
);
}
return obj[prop];
}
};
}
if (options.set) {
deepFreezer.set = function set(
obj: T,
prop: string,
_val: any,
_rec: Proxy<T>
): boolean {
throw new Error(`Can not set unknown prop "${prop}" on frozen object.`);
};
}
// $FlowIgnore for all useful purposes the output type is T here
return new Proxy(inputObj, deepFreezer);
}
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