对象没有变异

Question

Trying to mutate objects in a for loop.

I am expecting console.log(dish) to log the dish object with an ingredients property containing an array of unshifted ingredient s.

When I log dish.ingredients , it logs the ingredients.

When I log dish , it logs the dish objects without the ingredients.

Why is this?

for (let dish of dishArray) {
  dish['ingredients'] = []
  for (let ingredient of ingredientsArray) {
    if (dish._id.equals(ingredient._dishID)) {
      dish['ingredients'].unshift(ingredient)
    }
  }
  console.log(dish['ingredients'])             <------------- 
  console.log(dish)                            <-------------         
}

dishArray is an array of dish objects returned from a mongoose query.

Answer 1

Without further knowledge of your code, plain javascript == will do the job

 var dishArray = [{ _id: '0' }, { _id: '1' }]; var ingredientsArray = [{ _id: '0', _dishID: '0' }, { _id: '1', _dishID: '1' }]; for (let dish of dishArray) { dish['ingredients'] = []; for (let ingredient of ingredientsArray) { if (dish._id == ingredient._dishID) { dish['ingredients'].unshift(ingredient); } } console.log(dish['ingredients']); console.log(dish); }