Contract programming with typescript and decorators

Contract.ts

@In((a: string, b: string) => {
    assert(typeof a === 'string');
    assert(typeof b === 'string');
    assert(a.length > 5);
    assert(a.length > 7);
})
@Out((result: string) => {
    assert(typeof result === 'string');
    assert(a.length > 12);
})
export const myFunc = (a: string, b: string): string  => {
    return a + b;
}

//if possible

@In((a: string, b: string) => {
    assert(typeof a === 'string');
    assert(typeof b === 'string');
    assert(a.length > 5);
    assert(a.length > 7);
})
@Out((result: string) => {
    assert(typeof result === 'string');
    assert(a.length > 12);
})
function myFunc(a: string, b: string): string {
    return a + b;
}

@Invariant((myComp) => {
  assert(typeof myComp.props.name === 'string');
})
class MyComp extends React.Component {
    render() {
      <span>{this.props.name}</span>
    }
}

Hello! Could you rate my implementation of such decorators?
https://gist.github.com/SoEasy/5df7b9768463c44804d2773d043fd2fd
Sincerely, Vladimir.