js 怎么用find查找数组中符合条件的元素

const arr = [10, 20, 30, 40, 50];

// 查找第一个大于 25 的元素
const foundElement = arr.find(element => element > 25);

console.log(foundElement); // 输出: 30

// 如果没有找到符合条件的元素
const notFoundElement = arr.find(element => element > 50);

console.log(notFoundElement); // 输出: undefined

const arr = [10, 20, 30, 40, 50];

// 查找第一个大于 25 的元素的索引
const foundIndex = arr.findIndex(element => element > 25);

console.log(foundIndex); // 输出: 2

// 如果没有找到符合条件的元素
const notFoundIndex = arr.findIndex(element => element > 50);

console.log(notFoundIndex); // 输出: -1

const users = [
  { name: 'Alice', age: 25 },
  { name: 'Bob', age: 35 },
  { name: 'Charlie', age: 40 }
];

const firstUserOver30 = users.find(user => user.age > 30);

console.log(firstUserOver30); // 输出: { name: 'Bob', age: 35 }

const users = [
  { name: 'Alice', age: 25 },
  { name: 'Bob', age: 35 },
  { name: 'Charlie', age: 40 }
];

const usersOver30 = users.filter(user => user.age > 30);

console.log(usersOver30); // 输出: [{ name: 'Bob', age: 35 }, { name: 'Charlie', age: 40 }]

id

name

price

const products = [
  { id: 1, name: 'Laptop', price: 1200 },
  { id: 2, name: 'Keyboard', price: 100 },
  { id: 3, name: 'Mouse', price: 50 }
];

// 查找 id 为 2 的产品
const productWithId2 = products.find(product => product.id === 2);

console.log(productWithId2); // 输出: { id: 2, name: 'Keyboard', price: 100 }

// 查找价格大于 1000 的产品
const expensiveProduct = products.find(product => product.price > 1000);

console.log(expensiveProduct); // 输出: { id: 1, name: 'Laptop', price: 1200 }

// 查找价格大于 100 且名称包含 "Keyboard" 的产品 (虽然这里只有Keyboard满足)
const specificProduct = products.find(product => product.price > 80 && product.name.includes('Keyboard'));

console.log(specificProduct); // 输出: { id: 2, name: 'Keyboard', price: 100 }

const emptyArr = [];

const result = emptyArr.find(element => element > 10);

console.log(result); // 输出: undefined

const arr = [10, 20, 30];

const found = arr.find(element => element > 15);

console.log(found); // 输出: 20
console.log(arr);   // 输出: [10, 20, 30] (原始数组未被修改)

Array.prototype.find

if (!Array.prototype.find) {
  Array.prototype.find = function(callback) {
    if (this == null) {
      throw new TypeError('Array.prototype.find called on null or undefined');
    }
    if (typeof callback !== 'function') {
      throw new TypeError('callback must be a function');
    }
    var list = Object(this);
    var length = list.length >>> 0;
    var thisArg = arguments[1];
    for (var i = 0; i < length; i++) {
      if (callback.call(thisArg, list[i], i, list)) {
        return list[i];
      }
    }
    return undefined;
  };
}

const arr = [10, 20, 30, 40, 50];

let foundElement = undefined;
for (let i = 0; i < arr.length; i++) {
  if (arr[i] > 25) {
    foundElement = arr[i];
    break; // 找到第一个匹配项后需要手动停止循环
  }
}

console.log(foundElement); // 输出: 30

const arr = [10, 20, 30, 40, 50];

const foundElement = arr.find(element => element > 25);

console.log(foundElement); // 输出: 30