使用push和forEach创建数组和对象

Question

What's wrong with my code below? grandParent is undefined, what I want to achieve is each grandparent have a property of parent, and each parent have child (arrays of object too)

like so

[{
  name: 'a',
  parent: [{
    name: 'b',
    child: [{
      name: 'c'
    }]
  }]
}]

below code doesn't work

let grandParent = []

_.times(5, () => grandParent.push({
  name: faker.name.findName(),
  parent: []
}))

grandParent = grandParent.forEach(function(o) {
  return o.parent.push({ name: faker.name.findName() })
})

console.log(grandParent) //why here is undefined?

Answer 1

forEach doesn't return anything, you must use map instead. Also push returns the new size of the array, to return a new array use concat

grandParent = grandParent.map(function(o) {
  return o.parent.concat([{ name: faker.name.findName() }])
})

console.log(grandParent)

Other way to do it is to not return anything from forEach and just update the original array.

grandParent = grandParent.forEach(function(o) {
    o.parent.push({ name: faker.name.findName()})
})

console.log(grandParent)

Answer 2

From MDN docs of Array.prototype.forEach()

Return value: undefined

 let grandParent = [ { name: 'grandname0', parent: [] }, { name: 'grandname1', parent: [] }, { name: 'grandname2', parent: [] }, { name: 'grandname3', parent: [] }, { name: 'grandname4', parent: [] } ]; grandParent.forEach(function(o) { o.parent.push({ name: 'parent1' }); }); console.log(grandParent); 

Answer 3

.forEach does not return anything. using the map function will help. You code should look something like this.

let grandParent = []

_.times(5, () => grandParent.push({
  name: faker.name.findName(),
  parent: []
}))

grandParent = grandParent.map(function(o) {
  return o.parent.concat({ name: faker.name.findName() })
})

console.log(grandParent)