Get properties in Javascript Object

Question

I have the following javascript object that represents columns of a table that I want user can select to show and analyze based on his/her selection.

var nominalVars = {
 state : 'State', 
 messoreg : 'Messoreg',
 reggeoint : 'RegGeoInt',
 reggeoimd : 'RegGeoImed',
 microreg : 'Microreg',
 regmetro : 'RegMetro',
 city : 'City',
 tipdepe : 'TipDep',
 nvldepe : 'NvlDepe',
 prefix : 'Prefix',
 subord : 'Subord'
 };

What I need is to retrieve all the properties bellow the last checkbox checked, e.g., If the user selects [state] checkbox, then I want to get [messoreg], [reggeoint], [reggeoimd], [microreg], etc. and them passing the values to an Array.

I don't know if there is it another way to do that but I'm trying to avoid using Swith of If statements.

• Barmar: Don't use an object if ordering is important. Use an array.

Answer 1

You should never use an object if you want to keep track of the order. You can use a Map or an Array. The Map object holds key-value pairs and remembers the original insertion order of the keys.

let map = new Map();
map.set('state','State');
map.set('messoreg','Messoreg');
map.set('reggeoint','RegGeoInt');
map.set('reggeoimd','RegGeoImed');
map.set('microreg','Microreg');
map.set('regmetro','RegMetro');
map.set('city','City');
map.set('tipdepe','TipDep');
map.set('nvldepe','NvlDepe');
map.set('prefix','Prefix');
map.set('subord','Subord');
function getKeys(map, afterKey) {
 let shouldAdd = false, res = [];
 for (const key of map.keys()) {
 if (shouldAdd) res.push(key);
 if (key === afterKey) shouldAdd = true;
 }
 return res;
}
function getKeysBefore(map, beforeKey) {
 let shouldAdd = true, res = [];
 for (const key of map.keys()) {
 if (key === beforeKey) shouldAdd = false;
 if (shouldAdd) res.push(key);
 }
 return res;
}
//get keys after 'reggeoint'
let keys;
keys = getKeys(map, 'reggeoint');
document.write(JSON.stringify(keys))
//get keys after 'city'
keys = getKeys(map, 'city');
document.write(JSON.stringify(keys))
//get keys before 'city'
keys = getKeysBefore(map, 'city');
document.write(JSON.stringify(keys))

• Marcio Lino: Thank you! One more thing here. How can I do to get all options before the marked one? how would it be?
• rishabh0211: @user1460038 To get the keys before a particular key, you can modify the getKeys function a bit. I've added the getBeforeKeys function in the answer.
• Marcio Lino: In the case, if I need to retrieve both key and value to separate arrays I would need to create another array like "values[];" and use values.push(key)? That's correct?
• Marcio Lino: In the case, if I need to retrieve both key and value to separate arrays? I have tried like this ` for (var [key, value] of map) {console.log(key + " = " + value); ` but doesn't work
• rishabh0211: @user1460038 The way you mentioned above is correct if you want to access both keys and values. Destructure it by for(var [key, value] of map) and use key and value in the loop.

Answer 2

Object.keys(obj)

Will return the defined keys for any javascript-object. You'll have to filter this array accordingly to match your requirements.

Answer 3

Use Object.keys() to get the keys of an obect as an array. Then you can use indexOf() to get the index of a specific property, and you can slice the rest of the keys.

var nominalVars = {
 state: 'State',
 messoreg: 'Messoreg',
 reggeoint: 'RegGeoInt',
 reggeoimd: 'RegGeoImed',
 microreg: 'Microreg',
 regmetro: 'RegMetro',
 city: 'City',
 tipdepe: 'TipDep',
 nvldepe: 'NvlDepe',
 prefix: 'Prefix',
 subord: 'Subord'
};
let last_checkbox = "city";
let keys = Object.keys(nominalVars);
let index = keys.indexOf(last_checkbox);
let following_keys = keys.slice(index+1);
console.log(following_keys);

Note that only ES6 requires that the order of object properties to be maintained:

Does ES6 introduce a well-defined order of enumeration for object properties?

• Marcio Lino: I tried your suggestion here. It seems it only will work if I select the last option, in this case, state. If I choose [city] option, for example, the code bring me all the items above it, such as [regmetro], [microreg], and so on up to [state] option. I need to get only the option bellow city, such as [tipdepe], [nvldepe], [prefix] and [subord].
• Barmar: I changed my snippet to use city, it returns [ "tipdepe", "nvldepe", "prefix", "subord" ]
• Barmar: JavaScript doesn't require that Object.keys() return the keys in the same order that you defined them. You should use the array or Map solution.