remove an object the state array in react-ag捕鱼王app官网

to remove an object from the state array in react:

1. use filter()the method to iterate over an array.
2. in each iteration, check whether the condition is met.
3. sets state to filterthe new array returned by the method.

import {usestate} from 'react';
export default functionapp() {
  const initialstate = [
    {id: 1, name: '迹忆客', site: 'www.jiyik.com'},
    {id: 2, name: '百度', site: 'www.baidu.com'},
  ];
  const [employees, setemployees] = usestate(initialstate);
  const removesecond = () => {
    setemployees(current =>
      current.filter(employee => {
        // 👇️ remove object that has id equal to 2
        return employee.id !== 2;
      }),
    );
  };
  return (
    <div><buttononclick={removesecond}>remove secondbutton>
      {employees.map(({id, name, country}) => {
        return (
          <divkey={id}><h2>name: {name}h2><h2>country: {site}h2><hr />div>
        );
      })}
    div>
  );
}

we use usestatethe hook to initialize an employee state variable.

the function we pass to array.filterthe method will be called for each element in the array.

in each iteration, we check if the object's id property is not equal to 2 and return the result.

const initialstate = [
    {id: 1, name: '迹忆客', site: 'www.jiyik.com'},
    {id: 2, name: '百度', site: 'www.baidu.com'},
];
const filtered = initialstate.filter(obj => {
  // 👇️ returns truthy for all elements that
  // don't have an id equal to 2
  return obj.id !== 2;
});
// 👇️ [{id: 1, name: '迹忆客', site: 'www.jiyik.com'}]
console.log(filtered);

filterthe method returns a new array containing only those elements for which the callback function returns a true value.

if the condition is never met, array.filterthe function returns an empty array.

we setstatepass a function to , because that function is guaranteed to be called with the current (latest) state.

const removesecond = () => {
  // 👇️ current is the current state array
  setemployees(current =>
    current.filter(employee => {
      return employee.id !== 2;
    }),
  );
};

a function is passed to when calculating the next state using the previous state setstate.

otherwise, we could run into some weird race conditions if the state array we have access to doesn't represent the latest values.

if we need to remove objects from the state array based on multiple conditions, use logical and &&or logical or ||operators.

const initialstate = [
  {id: 1, name: '迹忆客', site: 'www.jiyik.com'},
  {id: 2, name: '百度', site: 'www.baidu.com'},
  {id: 3, name: 'google', site: 'www.google.com'},
];
const [employees, setemployees] = usestate(initialstate);
const remove = () => {
  setemployees(current =>
    current.filter(employee => {
      return employee.id !== 3 && employee.id !== 2;
    }),
  );
};

we have used the logical and &&operator, which will only return a true value if both conditions are met.

the callback function returns true only if the object's id property is not equal to 3 and not equal to 2 .

here is an ||example using the logical or operator.

const initialstate = [
  {id: 1, name: '迹忆客', site: 'www.jiyik.com'},
  {id: 2, name: '百度', site: 'www.baidu.com'},
  {id: 3, name: 'google', site: 'www.google.com'},
];
const [employees, setemployees] = usestate(initialstate);
const remove = () => {
  setemployees(current =>
    current.filter(employee => {
      return employee.name === 'alice' || employee.name === 'carl';
    }),
  );
};

either of the two conditions must evaluate to a truthy value for the element to be added to the new array.

in other words, if the name property of an object is equal to迹忆客or equal to百度, then the object will be added to the new array. all other objects are filtered out of the array.