How to set JavaScript object's property value?

Question

I have a JavaScript object that looks something like this:

obj = {
  person: {
    male: true,
    age: 10
  },
  state: {
    quit: false,
    rain: -3
  },
  game: {
     settings: {
       lang: 'en',
       os: 'win',
       ver: 10,
     },
  },
  next: 55,
  last: 10,
};

I'd like to create a function that can be used to set any of the obj's values like this:

function updateObj( property /*: string[]*/, value /*: any*/ ) {

  obj[property[0]][property[1]] = value;  <-- How to generalize? 

}

So then I can do things like:

updateObj( ['person', 'male'], false );
updateObj( ['state', 'rain'], 19 );

However the current implementation won't work properly if the property parameter length is not equal to 2. How can this line of code:

  obj[property[0]][property[1]] = value;

be generalized to work with any array size of property?

return if length is not greater or equal to 2 maybe ¯_(ツ)_/¯ — Aniket Navlur
– Aniket Navlur, Commented Oct 19, 2018 at 17:36
What else could you do? What do you wish to do if the length of property parameter is not greater than or equal to 2? — Aniket Navlur
– Aniket Navlur, Commented Oct 19, 2018 at 17:36
I'm not sure if I get it. If you know what the property names and the value are you can just use dot notation to set the value: obj.state.quit = false.What is the function meant to do that accessing the object directly can't? — Andy
– Andy, Commented Oct 19, 2018 at 17:36
I want updateObj(['game','settings','ver'], 11 ) and also updateObj(['next'], 100 ) to also work — Marek Krzeminski
– Marek Krzeminski, Commented Oct 19, 2018 at 18:19

Nitish Narang · Accepted Answer · 2018-10-19 18:16:38Z

2

Below method will achieve your result, used reduceRight below

// with reduceRight
function updateObj(prop, value) {
    prop  = prop.reverse()
    prop.reduceRight((o, d, i) => i == 0 ? (o[d] = value): o[d] , obj)
}

// with Reduce (efficient than above)
function updateObj(prop, value) {
    prop.reduce((o, d, i) => i == prop.length -1 ? (o[d] = value): o[d] , obj) 
}

updateObj( ['person', 'male'], false );
updateObj( ['state', 'rain'], 19 );

edited Oct 19, 2018 at 18:16

answered Oct 19, 2018 at 17:39

Nitish Narang

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3 Comments

Marek Krzeminski Over a year ago

why reverse and then use reduceRight, rather than just using reduce?

Nina Scholz Over a year ago

why twice a reverse?

Nitish Narang Over a year ago

Yes @MarekKnows.com It striked me first with reduceRight just to later realise I could do following as well prop.reduce((o, d, i) => i == prop.length -1 ? (o[d] = value): o[d] , obj)

Hero Wanders · Accepted Answer · 2018-10-19 17:43:42Z

1

Iterate over the property parts and for each one get the nested object:

function updateObj( property /*: string[]*/, value /*: any*/ ) {
    var base = obj;
    for (var i = 0; i < property.length - 1; i++) {
        base = base[property[i]];
    }
    base[property[property.length - 1]] = value;
}

answered Oct 19, 2018 at 17:43

Hero Wanders

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Comments

Nina Scholz · Accepted Answer · 2018-10-19 18:08:01Z

1

You could save the last key and reduce the object by taking the keys and return the last object reference. For not given properties assign an empty object.

At the end take the last key and assign the value.

function updateObj(properties, value) {
    var last = properties.pop();
    properties.reduce((o, k) => o[k] = o[k] || {}, obj)[last] = value;
}

var obj = { person: { male: true, age: 10 }, state: { quit: false, rain: -3 }, game: { settings: { lang: 'en', os: 'win', ver: 10 }, }, next: 55, last: 10 };

updateObj(['person', 'male'], false);
updateObj(['state', 'rain'], 19);
updateObj(['banana', 'ware'], 'snakeoil');


console.log(obj);

.as-console-wrapper { max-height: 100% !important; top: 0; }

answered Oct 19, 2018 at 18:08

Nina Scholz

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