immutable-state-nolib.ts

// without immutable
initialState.numbers = numbers.filter((num:number):boolean => {	
    return num % 2 === 0;
})

console.log('after update:', initialState); 
// after update: { numbers: [ 2, 4, 6 ] }

immutable-state-with-immutable.ts

// with immutable
initialState.numbers = numbers.filter((num:number):boolean => {	
    return num % 2 === 0;
})
// throws error: Cannot set on an immutable record.