使用JavaScript从数组访问元素名称（无值）

Question

Sorry if my question is bad. I'm stuck in the following simple javascript code:

var person={fname:"John",lname:"Doe",age:25};

for (x in person)
{
document.write(person[x] + " ");
}

The above code result is : John Doe 25

How do you show only value from lname element ? (with for (... in ...) statement)

I don't want to use person={"John","Doe",25} instead of one of above. I want to know how to access the element from array to get value.

Thank you

Edit: Thanks all for responses. This question was created because I have many items in array like :

        [{Name="A 1", Email="a1@manufacturer.com", Group="Group1"},
        {Name="A 2", Email="a2@manufacturer.com", Group="Group2"},
        {Name="A 3", Email="a3@manufacturer.com", Group="Group3"},
        {Name="B 1", Email="b1@manufacturer.com", Group="Group1"},
        {Name="V 1", Email="b1@manufacturer.com", Group="Group2"},
        {Name="X 1", Email="b1@manufacturer.com", Group="Group4"},
        {Name="Y 1", Email="b1@manufacturer.com", Group="Group3"},
        {Name="Z 1", Email="b1@manufacturer.com", Group="Group3"},
        {Name="W 1", Email="b1@manufacturer.com", Group="Group6"}]

I want to iterate this array and compare the element with my owned value. if object1.Group == 'Group3' { code }

Answer 1

What you have here is not an array, it is a JavaScript object. (In simple terms,) Arrays have numeric indexes, while objects have properties with property-name and value pairs.

To access a specific object property like "lname" simply say:

person.lname
// OR
person["lname"]

Or, if the name of the property you want to use is in a variable:

var whichProp = "lname";
person[whichProp]

With your data, to produce the output "John Doe" you'd say:

document.write(person.fname + " " + person.lname);

The for (x in person) syntax that you were using loops through every property of the person object, setting x to each property name in turn.

UPDATE FOR YOUR UPDATED QUESTION:

Assuming you have an array of objects:

var people = [{Name:"A 1", Email:"a1@manufacturer.com", Group:"Group1"},
              {Name:"A 2", Email:"a2@manufacturer.com", Group:"Group2"},
              {Name:"A 3", Email:"a3@manufacturer.com", Group:"Group3"},
              // etc ];

And you want to find the element where Group is "Group3" then you loop through the array with a traditional for loop as follows:

for (var i=0; i < people.length; i++) {
   if (people[i]["Group"] === "Group3") {
      // do something
   }
}

Within the if statement you can add a break statement if you want to stop processing after the first match. And of course you are free to use the people[i].Group syntax rather than people[i]["Group"] if you prefer it.

(Note also that your object literal syntax was incorrect in your question update: where you've used = you should've used : as shown in my answer above.)

Answer 2

var arr = [];
var person={fname:"John",lname:"Doe",age:25};
arr.push(person);

for (var i=0; i < arr.length; i++)
{
   document.write(arr[i].lname+ " ");
}

Update

JsFiddle example

Answer 3

您可以像这样访问person对象的两个属性fname和lname ：

document.write(person.fname + " " + person.lname);

Answer 4

That's not an Array, that's an Object. If you know the property you want to access, you don't need to iterate the Object. Just reference the property directly.

person.lname;

Edit: To iterate your Array and take action when the group matches:

for (var i = 0; i < objects.length; i++) {
    if (objects[i].Group == "Group3") {
        // do something 
    }
}

But, the code you posted is invalid. Property/value pairs are separated with a : , not = .