How to perform calculations to properties of a javascript object and print it out

Question

I am still learning javascript and this is NOT a homework problem.
I have an object collection

var x = [{name:'Ann',age:1,ending:'years old'},  
{name:'Bob',age:2,ending:'years old'},  
{name:'Cat',age:3,ending:'years old'},  
{name:'Dog',age:10,ending:'years old'},  
{name:'Fly',age:5,ending:'years old'}]

I want to know how to:
1, perform calculations to all 'age', such as age = age+1
2, put calculated data into object collection // x.push(age) I guess?
3, print out 'x' in this way:

    console.log(x[name]+' is '+x[age]+''+x[ending]+[calculations to age])
    //Ann is 1 years old2
    //Bob is 2 years old3....

I know the sentence doesn't make sense, but it doesn't matter.

My try:

var arr = '';

for (var property in x){
arr += x[property]+'\t';
}

var newArr = arr.split('\t')
,calculatedData = newArr[1]+1 ;
newArr.push(calculatedData) ;  
console.log(newArr[0]+' is '+newArr[1]+''+newArr[2]+calculatedData );

Your values for your name key aren't strings which will throw an error thinking they are undefined variables. — KrakenDev, Sep 09 '15 at 14:52
Side note: Your various names probably need to be in quotes, e.g. `name:"Ann"` rather than `name:Ann` (unless you happen to have a variable called `Ann`). — T.J. Crowder, Sep 09 '15 at 14:57

score 0 · Accepted Answer · edited May 23 '17 at 10:26

1, perform calculations to all 'age', such as age = age+1

What you're doing there is looping through an array. There are lots of ways to do that in JavaScript; see this answer for a long list. In modern JavaScript, forEach is common:

x.forEach(function(entry) {
    entry.age = entry.age + 1;
    // more commonly written like this:
    // ++entry.age;
});

Note how each array entry is given to our callback function as the first argument.

Or alternately, the venerable old for loop:

var index;
for (index = 0; index < x.length; ++index) {
    x[index].age = x[index].age + 1;
    // more commonly:
    // ++x[index].age;
}

Note how we have to look up the entry by index, x[index].

2, put calculated data into object collection // x.push(age) I guess?

Well, if we update age on the objects, it's already there. Alternately, we could create a new array with the results using map:

var newArray = x.map(function(entry) {
    return entry.age + 1;
});

Now, newArray is an array of numbers, the result of adding 1 to each age.

But based on your question #3, more likely you want to add a new property with the updated age:

x.forEach(function(entry) {
    entry.updatedAge = entry.age + 1;
});

3, print out 'x' in this way:

That's another loop:

x.forEach(function(entry) {
    console.log(entry.name + " is " + entry.age + " " + entry.ending + " " + entry.updatedAge);
});

Live Example:

var x = [{name:"Ann",age:1,ending:'years old'},  
{name:"Bob",age:2,ending:'years old'},  
{name:"Cat",age:3,ending:'years old'},  
{name:"Dog",age:10,ending:'years old'},  
{name:"Fly",age:5,ending:'years old'}];

x.forEach(function(entry) {
  entry.updatedAge = entry.age + 1;
});

x.forEach(function(entry) {
  snippet.log(entry.name + " is " + entry.age + " " + entry.ending + " " + entry.updatedAge);
});

<!-- Script provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 -->
<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>

You can, of course, do it all in one loop:

x.forEach(function(entry) {
  snippet.log(entry.name + " is " + entry.age + " " + entry.ending + " " + (entry.age + 1));
  // Note the () ----------------------------------------------------------^-------------^
});

Live Example:

var x = [{name:"Ann",age:1,ending:'years old'},  
{name:"Bob",age:2,ending:'years old'},  
{name:"Cat",age:3,ending:'years old'},  
{name:"Dog",age:10,ending:'years old'},  
{name:"Fly",age:5,ending:'years old'}];

x.forEach(function(entry) {
  snippet.log(entry.name + " is " + entry.age + " " + entry.ending + " " + (entry.age + 1));
});

<!-- Script provides the `snippet` object, see http://meta.stackexchange.com/a/242144/134069 -->
<script src="http://tjcrowder.github.io/simple-snippets-console/snippet.js"></script>

Sionnach733 · Answer 2 · 2015-09-09T15:03:42.963

Iterate through the collection and perform you calculation per each iteration:

var x = [{name:"Ann",age:1,ending:'years old'},  
{name:"Bob",age:2,ending:'years old'},  
{name:"Cat",age:3,ending:'years old'},  
{name:"Dog",age:10,ending:'years old'},  
{name:"Fly",age:5,ending:'years old'}];

for(var i = 0; i<x.length; i++){
   //perform calc on age
   x[i].age = x[i].age + 1;
   //print info in object
   console.log(x[i].name+' is '+x[i].age+' '+x[i].ending); 
}

How to perform calculations to properties of a javascript object and print it out

2 Answers2