foreach循环和返回undefined的值

Question

我想知道是否有人能解释我为什么这个函数返回undefined而不是创建对象

var people = [
  {name: 'John'},
  {name: 'Dean'},
  {name: 'Jim'}
];

function test(name) {
  people.forEach(function(person){
    if (person.name === 'John') {
      return person;
    }   
  });
}

var john = test('John');
console.log(john);

// returning 'undefined'

Answer 1

返回forEach循环不起作用,你在forEach回调函数上,而不是在test()函数上.因此,您需要从forEach循环外部返回值.

var people = [{
  name: 'John'
}, {
  name: 'Dean'
}, {
  name: 'Jim'
}];

function test(name) {
  var res;
  people.forEach(function(person) {
    if (person.name === 'John') {
      res = person;
    }
  });
  return res;
}

var john = test('John');
console.log(john);

或者从数组中查找单个元素使用find()

var people = [{
  name: 'John'
}, {
  name: 'Dean'
}, {
  name: 'Jim'
}];

function test(name) {
  return people.find(function(person) {
    return person.name === 'John';
  });
}

var john = test('John');
console.log(john);