如何在数组中查找元素

Question

I'm really new to javascript and I have an array of objects.

var cart = [
  { id: 1, price: 2 },
  { id: 2, price: 1 }
];

and I'm using a for loop to find the ID:

for (var i = 0; i < cart.length; i++) {
  if (cart[i].id === id) {
    return cart[i]
  }
}

return null;

I know there's functions like find() , but I'm not too sure on how to use that. Can anyone help?

Answer 1

With find , you might need babel , but just the code you need:

ES6

const id = 1;
const found = cart.find(item => item.id === id)

Vanilla

var id = 1;
var found = cart.find(function(item) {return item.id === id})

find takes a function (in our case with es6: () => {} is an anonymous function), and applies it to every item in the list, until it finds the first match, how does it know when it is a match: once your function returns true, then it cuts the loop, and returns the item.

HOWEVER

Another option, that does not use find but might be more readable than a traditional for loop:

var id = 1;
for(var item in cart) {
  if(item.id == id) {
    return item;
  }
}
return null

There are also a slew of libraries out there that can help you achieve this on different ways, ex: underscore.js , lodash , which I will not cover, but you can take a look at if you are really interested.

Answer 2

You are right. There is a function called find . You can set up the callback function to use with find , and even set it up to accept a parameter (such as the id ):

 var cart = [{ id: 1, price: 2 }, { id: 2, price: 1 }]; function byID(id) { return function(element) { return element.id == id; } } var item = cart.find(byID(2)); console.log(item); 

With issues like this, I very much appreciate the library lodash . It allows you to do things like so:

 var cart = [{id: 1, price: 5}, {id: 2, price: 6}]; var item = _.find(cart, {id:2}); console.log(item); 

 <script src="https://cdn.jsdelivr.net/lodash/4.17.4/lodash.min.js"></script>