Need elegant way to extract value as String from json maps in Javascript

Question

I am a JS newbie trying to extract some value from an array of json maps. The map is something like:

var  tags = [{
    Key: 'backup',
    Value: 'true'
  },
  {
    Key: 'Name',
    Value: 'sdlc-root'
  }
]

// Here is my first attempt:

var volName = tags.filter(function(item) {
    return item.Key === 'Name';
  })
  .map(result => {
    return result.Value;
  });
console.log(volName);

The result is: [ 'sdlc-root' ] , but I only need the String value.

The temporary solution I take for now is:

var volName = tags.filter(function(item) { return item.Key === 'Name'; })
                  .map(result => { return result.Value; })**[0]**;
console.log(volName);

The result is: sdlc-root

I hate my temporary solution, and would like to hear some advice for improvement or alternatives from experienced developers

Easy solution: destructure var [volName] = More elegant solution: use .find — CertainPerformance
– CertainPerformance, Commented Dec 18, 2018 at 9:14
@NinaScholz I have multiple elements, above is just example, tks. — GreenLake4964
– GreenLake4964, Commented Dec 18, 2018 at 9:23
@CertainPerformance not sure if my JS version support 'find', I think it's relatively new? Will definitely give a try. tks. — GreenLake4964
– GreenLake4964, Commented Dec 18, 2018 at 9:24
Don't let obsolete browsers cripple your ability to write concise, clean code - if an environment doesn't support ES6, use Babel + polyfills. — CertainPerformance
– CertainPerformance, Commented Dec 18, 2018 at 9:25

Nina Scholz · Accepted Answer · 2018-12-18 09:16:26Z

5

You could find the element or a default object and take the wanted property.

var volName = (tags.find(({ Key }) => Key === 'Name') || {}).Value;

edited Dec 18, 2018 at 9:16

answered Dec 18, 2018 at 9:14

Nina Scholz

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4 Comments

Ben Fortune Over a year ago

This is going to err if it doesn't find the correct value.

Nina Scholz Over a year ago

@chŝdk, you get from an empty object with a not given property the value undefined. this does not throw an error.

mplungjan Over a year ago

Why the ({Key}) - this seems easier to understand, no? var volName = (tags.find(x => x.Key === "Name") || {}).Value has less brackets

Nina Scholz Over a year ago

@mplungjan i think, if you need only a single property, you could destructure this property and show that you use only this property. it prevents as well an assignment to the object, if the value is a primitive value.

mplungjan · Accepted Answer · 2018-12-18 09:31:57Z

3

Write a custom function like below

var tags = [{
    Key: 'backup',
    Value: 'true'
  },
  {
    Key: 'Name',
    Value: 'sdlc-root'
  }
]

function f(tags) {
  for (i = 0; i <= tags.length; i++) {
    if (tags[i] && tags[i]['Key'] === 'Name') {
      return tags[i]['Value']
    }
  }
}

console.log(f(tags))

edited Dec 18, 2018 at 9:31

mplungjan

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answered Dec 18, 2018 at 9:24

anjaneyulubatta505

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Comments

jorbuedo · Accepted Answer · 2018-12-18 09:34:08Z

0

const tagsObj = tags.reduce((a, c) => { a[c.Key] = c.Value; return a }, {})
// {backup: "true", Name: "sdlc-root"}
console.log(tagsObj["Name"])
// "sdlc-root"

answered Dec 18, 2018 at 9:34

jorbuedo

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