The sample code in the doc docs not compile.

const ABRecord = imm.Record({ a: 1, b: 2 })
const myRecord = new ABRecord({ b: 3 })
let x_a = myRecord.get('a') // compile error: 2 arguments expected, only 1 received

The reason is that Record.get() is defined as

get<K extends keyof TProps,D>(key: K, notSetValue: any): TProps[K];

Argument notSetValue faces 2 issues

• it is required (both js implementation and doc consider it to be optional : "notSetValue will be returned if provided")
• notSetValue should not be any :
• either is should be required to have the same type as the property (solution implemented in this PR)
• or be typed as a generic parameter (see alternative solution below)

Alternative solution

get<K extends keyof TProps, D>(key: K, notSetValue?: D): TProps[K] | D;