React-对象作为React子对象无效

Question

I am trying to create the stop watch on the reactive js. Below is my code

 <div id="root"></div> <script src="https://unpkg.com/react@16.3.1/umd/react.development.js"></script> <script src="https://unpkg.com/react-dom@16.3.1/umd/react-dom.development.js"></script> <script src="https://unpkg.com/babel-standalone@6.26.0/babel.js"></script> <script src="https://unpkg.com/prop-types@15.6.1/prop-types.js"></script> <script type="text/babel"> function StopWatch(running, lapse) { const buttonStyles = { border: "1px solid #ccc", background: "#fff", fontSize: "2em", padding: 15, margin: 5, width: 200 }; return ( <div> <label style={{ fontSize: "5em", display: "block" }} > {lapse}ms </label> <button style={buttonStyles}>{running ? "stop" : "start"}</button> <button style={buttonStyles}>Clear</button> </div> ); } const rootElement = document.getElementById("root"); const element = <StopWatch running={true} lapse={0} />; ReactDOM.render(element, rootElement); </script> 

While executing above file, i am getting the error message:

Uncaught Invariant Violation: Objects are not valid as a React child (found: object with keys {}). If you meant to render a collection of children, use an array instead.

My concern is that I am able to pass the value for the property running , but the error happen when I am passing the value for the property lapse . What is the issue here and what is the difference on passing the value for both properties?

Answer 1

Your functional Component receives props as the first argument.

It should be something like this with object destructuring

<script type="text/babel">
function StopWatch({ running, lapse }) {
  const buttonStyles = {
    border: "1px solid #ccc",
    background: "#fff",
    fontSize: "2em",
    padding: 15,
    margin: 5,
    width: 200
  };
  return (
    <div>
      <label
        style={{
          fontSize: "5em",
          display: "block"
        }}
      >
        {lapse}ms
      </label>

      <button style={buttonStyles}>{running ? "stop" : "start"}</button>
      <button style={buttonStyles}>Clear</button>
    </div>
  );
}
const rootElement = document.getElementById("root");
const element = <StopWatch running={true} lapse={0} />;
ReactDOM.render(element, rootElement);

</script>

Answer 2

You forgot to put the curly brackets while passing the props; it should be:

function StopWatch({ running, lapse })