One liner javascript function to edit value of specific property from array of objects

Question

Say, I have array of objects:

arr = [
    {path: 'mexico', name: 'mexico'},
    {path: 'brazil', name: 'brazil'},
    {path: 'netherlands', name: 'netherlands'}
];

What I want to achieve:

prefix = 'country/'
arr = [
    {path: 'country/mexico', name: 'mexico'},
    {path: 'country/brazil', name: 'brazil'},
    {path: 'country/netherlands', name: 'netherlands'}
];

Is there a one liner javascript function that append the prefix country/ into the path property of all objects in the array?

perhaps, something like this: arr.append(prefix, arr, 'path');

You could just do something like arr.forEach(x => x.path = "country/" + path) — nick zoum
– nick zoum, Commented Apr 15, 2022 at 7:10

Giovanni Esposito · Accepted Answer · 2022-04-15 08:07:07Z

2

You could use a forEach and a concat:

arr = [
    {path: 'mexico', name: 'mexico'},
    {path: 'brazil', name: 'brazil'},
    {path: 'netherlands', name: 'netherlands'}
];
prefix = 'country/';
arr.forEach(x => x.path = prefix.concat(x.path));
console.log(arr);

EDIT:

Following what @MaikLowrey suggested on comment and reading this answer, + operator to concat strings has better performance and memory allocation compared to concat operator.

So the optimized solution is:

    arr = [
        {path: 'mexico', name: 'mexico'},
        {path: 'brazil', name: 'brazil'},
        {path: 'netherlands', name: 'netherlands'}
    ];
    prefix = 'country/';
    arr.forEach(x => x.path = prefix + x.path);
    console.log(arr);

edited Apr 15, 2022 at 8:07

answered Apr 15, 2022 at 7:13

Giovanni Esposito

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3 Comments

Maik Lowrey Over a year ago

Good solution but concat decrease your perfomance. better use +. x.path = prefix + x.path)

Giovanni Esposito Over a year ago

@MaikLowrey this is an intersting point of discussion. Unfortunately I'm not so expert to say which is the faster one. I read this answer. Is quite old but it was updated on 2017. Before that date seems that concat works better with few strings, but on 2017 update seems that + got a small advantage in terms of performance and memory allocation. So yes, you are right. i will update my answer.

Maik Lowrey Over a year ago

Thank you for your feedback. It was only a hint. But if you work on scaled application it could be a point for optimization. ... and i like to discuss programming :-) Greetings & +1up!

StepUp · Accepted Answer · 2022-04-15 07:15:49Z

2

As mdn says about map() function:

The map() method creates a new array populated with the results of calling a provided function on every element in the calling array.

So the code would be looked like that:

arr = arr.map(s => ({...s, path: 'country/' + s.path}))

An example:

let arr = [
    {path: 'mexico', name: 'mexico'},
    {path: 'brazil', name: 'brazil'},
    {path: 'netherlands', name: 'netherlands'}
];

arr = arr.map(s => ({...s, path: 'country/' + s.path}))
console.log(arr)

edited Apr 15, 2022 at 7:15

answered Apr 15, 2022 at 7:10

StepUp

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1 Comment

true_k Over a year ago

This should be a right answer

Vincent · Accepted Answer · 2022-04-15 07:10:23Z

0

arr = [
    {path: 'mexico', name: 'mexico'},
    {path: 'brazil', name: 'brazil'},
    {path: 'netherlands', name: 'netherlands'}
];

prefix = "country/"

arr.forEach(entry => entry.path = prefix + entry.path)
console.log(arr)

answered Apr 15, 2022 at 7:10

Vincent

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Comments

nick zoum · Accepted Answer · 2022-04-15 07:25:25Z

The easiest way to do this would to use Array#forEach or Array#map like so:

var prefix = 'country/';
var arr = [{
    path: 'mexico',
    name: 'mexico'
  },
  {
    path: 'brazil',
    name: 'brazil'
  },
  {
    path: 'netherlands',
    name: 'netherlands'
  }
];
arr.forEach(item => item.path = prefix + item.path);
console.log(arr);

You could also create your own somewhat generic function to do this for you

var prefix = 'country/';
var arr = [{
    path: 'mexico',
    name: 'mexico'
  },
  {
    path: 'brazil',
    name: 'brazil'
  },
  {
    path: 'netherlands',
    name: 'netherlands'
  }
];
console.log(listPrepend(arr, "path", prefix));


function listPrepend(list, property, prefix) {
  return list.map(function(item) {
    item[property] = prefix + item[property];
    return item;
  });
}

You could also add some more logic to it

var prefix = 'country/';
var arr = [{
    path: 'mexico',
    name: 'mexico',
    nested: {
      path: 'mexico'
    }
  },
  {
    path: 'brazil',
    name: 'brazil',
    nested: {
      path: 'brazil'
    }
  },
  {
    path: 'netherlands',
    name: 'netherlands',
    nested: {
      path: 'netherlands'
    }
  }
];
console.log(listPrepend(arr, "nested.path", prefix));


function listPrepend(list, propertyPath, prefix) {
  return list.map(function(item) {
    propertyPath.split(".").reduce(function(result, property, index, full) {
      var innerValue = result[property];
      if (index === full.length - 1) {
        result[property] = prefix + innerValue;
        return result;
      }
      return innerValue;
    }, item);
    return item;
  });
}

Maik Lowrey · Accepted Answer · 2022-04-15 07:56:26Z

All conceivable possibilities are already listed. Therefore here is a slightly different approach. Why fill your existing array with unnecessary redudant strings, when you can add the string in front in your loop. The advantage is not obvious in this example. If you have an array of more than just 195 countries, then you have unnecessarily included x times the prefix. Unnecessary power! ;-)

const arr = [
    {path: 'mexico', name: 'mexico'},
    {path: 'brazil', name: 'brazil'},
    {path: 'netherlands', name: 'netherlands'}
  ];
const prefix = 'country/';

function setPath(row) {
  return  prefix + row.path;  
}

// in the loop
arr.forEach(row => console.log(setPath(row)))

// by index
console.log(`Here is the link to ${arr[1].name}: ${setPath(arr[1])}`)

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