How to sort objects from js array, by object key/value

Question

I have an array which contains many objects. I am trying to sort the array based on the key value of each object.

So, the object looks like this:

var info = [ 
    {name: 'Adam', age: '1987-01-09T18:23:20.000Z'}, 
    {name: 'Issac', age: '1988-09-02T11:17:11.000Z'}, 
    {name: 'Tom', age: '2003-08-07T13:07:03.000Z'}, 
    {name: 'Jane', age: '1997-17-01T14:57:41.000Z'} 
];

I am trying saved the new (sorted) data into a variable called sorted;

 var sorted = info.forEach(function(person) {
    var age = moment(String(person.age)).format('MM/DD/YYYY'); 

    return age 

    }, this);


 console.log(sorted)

So, I have momentjs, to change the date into a time format that can easily be sorted, but the sorted console.log shows me undefined.

Honestly, I don't even know how sorting functions work. At least it should return the age from the loop and thus console.log() should not have been empty

forEach returns undefined, map would be what returns a new array — MackoyokcaM
– MackoyokcaM, Commented Sep 29, 2017 at 16:56
You could write your own comparator for native sort, or use something like lodash: _.sortBy(info, ['name', 'age']); -- lodash.com/docs/4.17.4#sortBy — lux
– lux, Commented Sep 29, 2017 at 16:57

maowtm · Accepted Answer · 2017-09-29 17:03:03Z

2

forEach isn't used to sort, neither is it used to change an array. For sorting, you should use sort.

The sort function sorts an array by comparing elements in pairs. You need to give it a function that will "compare" two elements. The "compare" function takes in two argument a and b, and should return a negative number if a<b, 0 if they are the same, and a positive number if a>b.

Therefore, the code below could works:

var info = [ 
    {name: 'Adam', age: '1987-01-09T18:23:20.000Z'}, 
    {name: 'Issac', age: '1988-09-02T11:17:11.000Z'}, 
    {name: 'Tom', age: '2003-08-07T13:07:03.000Z'}, 
    {name: 'Jane', age: '1997-12-01T14:57:41.000Z'} 
];

info.sort(function (a, b) {
    return (new Date(a.age)).getTime() - (new Date(b.age)).getTime()
})

Also notice that the fourth date you have given - 1997-17-01T14:57:41.000Z, is invalid since month number must be less than 13.

answered Sep 29, 2017 at 17:03

maowtm

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4 Comments

Sebastian Simon Over a year ago

1997-17-01T14:57:41.000Z is valid in YYYY-DD-MM format, which is quite non-standard and unexpected…

maowtm Over a year ago

> new Date('1997-17-01T14:57:41.000Z') => Invalid Date Looks like at least chrome doesn't support this.

Sebastian Simon Over a year ago

I know, this is an Invalid Date in JavaScript. The OP, however, is trying to parse this as a YYYY-DD-MM date in moment.js. It would be valid as such, but it goes against the standard, because YYYY-AA-BB should always be YYYY-MM-DD which is standardized in ISO 8601.

maowtm Over a year ago

@Xufox Oh… Good point - Moment.js actually supports this? Haven't looked up but I have a feeling that this is going to result in non-obvious bugs.

Kunvar Singh · Accepted Answer · 2017-09-29 17:12:14Z

0

Try for this:

var arrayOfObject = [ 
    {name: 'Adam', age: '1987-01-09T18:23:20.000Z'}, 
    {name: 'Issac', age: '1988-09-02T11:17:11.000Z'}, 
    {name: 'Tom', age: '2003-08-07T13:07:03.000Z'}, 
    {name: 'Jane', age: '1997-12-01T14:57:41.000Z'} 
];

arrayOfObject.sort(function (a, b) {
    return ((new Date(a.age)).getTime() - (new Date(b.age)).getTime());
})

edited Sep 29, 2017 at 17:12

answered Sep 29, 2017 at 17:08

Kunvar Singh

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1 Comment

maowtm Over a year ago

Wait a minute… The syntax, even the parentheses are the same. What a coincidence.

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