Promise Merge

Requirements

• Export promiseMerge as named and default. Accept two promises or thenables and return a Promise for their merged results.
• Add two numbers; concatenate two strings in input order; concatenate two arrays into a new array; shallow-merge two plain objects into a new object with right keys taking precedence.
• Both results must have the same supported category. Null, booleans, dates, and mismatched categories reject with TypeError. Null-prototype plain objects are supported.
• Observe both inputs concurrently. Reject with the exact reason as soon as either rejects, without waiting for the other.
• Do not mutate values. Preserve nested references. Promise.all is allowed.

Examples

Input: await promiseMerge(Promise.resolve([1, 2]), Promise.resolve([3]));
Output: [1, 2, 3]