Type ‘string’ has no properties in common with type ‘properties‘

An error occurs because the type ‘string’ does not have any properties in common with the type ‘properties<string | number, string & {}>’.

This means that the ‘string’ type does not satisfy the requirement of having any shared properties with the ‘properties<string | number, string & {}>’ type.

To better understand this, let’s consider an example:

    
      type properties<K, V> = {
        key: K;
        value: V;
      };

      const example: properties<string | number, string & {}> = {
        key: 123, // valid: key can be either string or number
        value: "Hello" // valid: value must be a string
      };

      const value: string = example.value; // valid
      const key: string = example.key; // invalid: example.key can be either string or number
      const anotherKey: number = example.key; // invalid: example.key can be either string or number
    
  

In the above example, we define a type called ‘properties’ which has two generic parameters ‘K’ and ‘V’. It has two properties ‘key’ of type K and ‘value’ of type V.

We then create a constant called ‘example’ of type ‘properties<string | number, string & {}>’. This means that the ‘key’ property can be either a string or a number, and the ‘value’ property must be a string.

However, when we try to assign the value of ‘example.key’ to a variable of type string, it is invalid because ‘example.key’ can be either a string or a number. Similarly, assigning it to a variable of type number is also invalid.