reactjs

Basic idea is: Use controlled component (use value and onChange property of input field), and inside onChange handle check whether the entered value is proper number or not. Update the state only when entered value is a valid number. For that use this regex: /^[0-9\b]+$/; onChange handler will be: onChange(e){ const re = /^[0-9\b]+$/; // … Read more

What you did is correct apart from the event name and the fact that alert will be blocked in that particular event. You can show a message like this: window.addEventListener(“beforeunload”, (ev) => { ev.preventDefault(); return ev.returnValue=”Are you sure you want to close?”; }); Hope this helps.

setState is an async function. React may batch a bunch of setStates together. So the value of this.state.count is the value at the time you make the request. A better solutions to call a function that gets evaluated at the time the setState gets executed. this.setState((prevState, props) => ({ counter: prevState.counter + 1 })); from … Read more

As noted above: The React way would be to pass callbacks down to children explicitly via props — . There’s no support for custom events w/ bubbling in React. The reactive programming abstraction is orthogonal: Programming interactive systems by means of the observer pattern is hard and error-prone yet is still the implementation standard in … Read more

To ensure that the implicit browser state you mention and state of children is reset, you can add a key attribute to the root-level component returned by render; when it changes, that component will be thrown away and created from scratch. render: function() { // … return <div key={uniqueId}> {children} </div>; } There’s no shortcut … Read more