向对象数组中的每个对象添加新元素

Question

Suppose I have this:

var names = [
{
    "First": "Jim",
    "Last": "Jones"
},
{
    "First": "Mike",
    "Last": "Smith"
},
{
    "First": "Joe",
    "Last": "Johnson"
}
]

And I now want to add a "Middle" field with a middle name to each object in that array. Can I do it simply? Push doesn't seem to exist in this scenario.

Answer 1

You can just assign it, using obj.Middle or obj["Middle"] :

But if you want the ordering to be really the middle one, then it can't, because ES6 property names are ordered first by numbers (as strings) and then by insertion order.

 var names = [{ "First": "Jim", "Last": "Jones" }, { "First": "Mike", "Last": "Smith" }, { "First": "Joe", "Last": "Johnson" } ]; names.forEach(obj => obj.Middle = "N/A"); console.log(names);

Answer 2

You can use the .map method on the Array object to create a new array without mutating the original array.

push adds a new entry to the array and does not update the item.

 var names = [{ "First": "Jim", "Last": "Jones" }, { "First": "Mike", "Last": "Smith" }, { "First": "Joe", "Last": "Johnson" } ]; var updatedNames = names.map(name => { const { First, Last } = name; return { First, Last, Middle : 'middle name' } }); console.log(updatedNames);

Answer 3

map method of the javascript can be used to achieve this,

let newNamesArray = names.map(name => {
  return {
    ...name,
    "Middle": "The middle name you want"
  }
});
names = newNamesArray;

Answer 4

You can also achieve it by using .assign method of Object and .map of Array this way

 var names = [{ "First": "Jim", "Last": "Jones" }, { "First": "Mike", "Last": "Smith" }, { "First": "Joe", "Last": "Johnson" } ]; names = names.map(obj => Object.assign({}, obj, {Middle: "N/A"})); console.log(names);

Note that is very useful if you want to separate the obtained names to the old ones For that, instead of affecting the result to names simply create another variable

let anotherNames = names.map(obj => Object.assign({}, obj, {Middle: "N/A"}));

As I said the anotherNames and Names variable are totally independent