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deepMerge.ts
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deepMerge.ts
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type ObjectLike<T = unknown> = Record<string, T>;
/**
* Check if the variable contains an object strictly rejecting arrays
* @param obj an object
* @returns `true` if obj is an object
*/
function isObjectNotArray<T extends ObjectLike>(
obj: unknown | unknown[],
): obj is T {
return typeof obj === 'object' && obj != null && !Array.isArray(obj);
}
/**
* Pure function - doesn't mutate either parameter!
* Merges two objects together deeply, overwriting the properties in first with the properties in second
* @param first The first object
* @param second The second object
* @returns a new object
*/
export function deepMerge(
first: ObjectLike = {},
second: ObjectLike = {},
): Record<string, unknown> {
// get the unique set of keys across both objects
const keys = new Set(Object.keys(first).concat(Object.keys(second)));
return Array.from(keys).reduce<ObjectLike>((acc, key) => {
const firstHasKey = key in first;
const secondHasKey = key in second;
const firstValue = first[key];
const secondValue = second[key];
if (firstHasKey && secondHasKey) {
if (isObjectNotArray(firstValue) && isObjectNotArray(secondValue)) {
// object type
acc[key] = deepMerge(firstValue, secondValue);
} else {
// value type
acc[key] = secondValue;
}
} else if (firstHasKey) {
acc[key] = firstValue;
} else {
acc[key] = secondValue;
}
return acc;
}, {});
}
export { isObjectNotArray };