From your examples, I assume that those digits should be in the correct places too.

As you have not provided an example with a case where user input is shorter than the random number, I'll assume that in this case such option either does not exist or you are handling it in some other way.

Now that my assumptions are defined, you can do this by iterating over user input number by converting it to a string and comparing symbols one by one. You need to check if the symbol at position i is equal in both numbers (input[i] === random_num[i]), just don't forget that while iterating over input, you can increase i beyond the length of random_num, you should check those cases and mark as wrong every input[i] where i > random_num.length

This is my attempt

class NumberMemoryGame extends React.Component {
  constructor(props) {
    super(props);
    this.state = {value: '', answer: '123456'};

    this.handleChange = this.handleChange.bind(this);
    this.handleSubmit = this.handleSubmit.bind(this);
  }

  handleChange(event) {
    this.setState({value: event.target.value});
  }

  handleSubmit(event) {
    event.preventDefault();
  }

  render() {
    return (
        <div>
        <form onSubmit={this.handleSubmit}>
          <label>
            Guess:
            <input type="text" value={this.state.value} onChange={this.handleChange} />
          </label>
          <input type="submit" value="Submit" />
        </form>
        <div>
          {[...this.state.value].map((char, i) => (
          <span className={`${(char === this.state.answer[i]) ? 'right' : 'wrong'}`}>
           {char}
          </span>))}
        </div>
      </div>
    );
  }
}

You can find the JS Fiddle here.

Assuming you are passing both the entries as arrays to a component and let say array_1 is the original entry and array_2 is the second entry, then all you got to do is

function App({ array_1, array_2 }) {
  return (
    <div>
      {array_2.map((val, i) => {
        if (val === array_1[i]) {
          return <span>{val}</span>;
        }
        return <span className="wrong">{val}</span>;
      })}
    </div>
  );
}