How can I retrieve the keys of a JavaScript object as an array, using either jQuery or pure JavaScript?
Is there a more concise approach than this?
var data = { 'first' : 'apple', 'second' : 'banana' };
var elements = [];
for (var item in data) {
elements.push(item);
}
Utilize the Object.keys method:
var example = {
'apple': 'banana',
'cat': 'dog'
};
var keys = Object.keys(example);
console.log(keys) // ['apple', 'cat']
// (or another order, as keys are not guaranteed to be ordered).This functionality belongs to ES5. It is supported by modern browsers but may not work in older browsers. Check compatibility here.
You can find an implementation of Object.keys in the ES5-shim library
To utilize jQuery's $.map, you can do the following:
var animals = { 'alpha' : 'cat', 'beta' : 'dog' },
keys = $.map(animals, function(value, index){
return index;
});
Undoubtedly, utilizing Object.keys() is considered the most efficient method to retrieve an Object's keys. In case it is not supported in your environment, it can be easily replicated using a code snippet similar to the one in your example (with the exception that you must consider the fact that your loop will traverse through all properties in the prototype chain, unlike the behavior of Object.keys()).
Nevertheless, the code snippet you provided...
var foo = { 'alpha' : 'puffin', 'beta' : 'beagle' };
var keys = [];
for (var key in foo) {
keys.push(key);
}
See it in action on jsFiddle.
...can be optimized. You can directly assign the keys within the declaration of the variable.
var foo = { 'alpha' : 'puffin', 'beta' : 'beagle' };
var keys = [], i = 0;
for (keys[i++] in foo) {}
View the revised version on jsFiddle.
Nevertheless, this behavior varies from what Object.keys() actually does (jsFiddle). In such cases, you can simply refer to the shim provided in the MDN documentation.
If you're seeking a way to extract the keys of a deeply nested object into a flat array, you've come to the right place:
const extractObjectKeys = (obj, prefix = '') => {
return Object.entries(obj).reduce((keyArray, [key, val]) => {
const newKeys = [ ...keyArray, prefix ? `${prefix}.${key}` : key ]
if (Object.prototype.toString.call(val) === '[object Object]') {
const newPrefix = prefix ? `${prefix}.${key}` : key
const otherKeys = extractObjectKeys(val, newPrefix)
return [ ...newKeys, ...otherKeys ]
}
return newKeys
}, [])
}
console.log(extractObjectKeys({a: 1, b: 2, c: { d: 3, e: { f: 4 }}}))Attempting to condense this code onto a single line, inspired by the challenge of creating a one-liner. Not sure about the Pythonic nature of it though ;)
var keys = (function(o){var ks=[]; for(var k in o) ks.push(k); return ks})(foo);
To retrieve all keys from an Object, utilize the Object.keys() method. This function accepts an object as input and outputs an array containing all the keys.
const object = {
a: 'string1',
b: 42,
c: 34
};
const keys = Object.keys(object)
console.log(keys);
console.log(keys.length) // obtain the total number of properties in the objectIn the example above, we capture the keys in an array called 'keys'. By checking the length of the 'keys' array, we can easily determine the number of properties in the object.
Object.values()The counterpart to Object.keys() is Object.values(). This function accepts an object as input and outputs an array of values. For instance:
const object = {
a: 'random',
b: 22,
c: true
};
console.log(Object.values(object));Why is it that in the year 2022, JavaScript still lacks a reliable way to handle hashes?
Although this workaround issues a warning, it gets the job done:
Object.prototype.keys = function() { return Object.keys(this) }
console.log("Keys of an object: ", { a:1, b:2 }.keys() )
// Keys of an object: Array [ "a", "b" ]
// WARN: Line 8:1: Object prototype is read only, properties should not be added no-extend-native
However, it's worth noting that Extending Built-in Objects is a Controversial Practice.
When opting for Underscore.js, make sure to follow this code snippet:
var animals = { 'cat' : 'meow', 'dog' : 'woof' };
var animalSounds = [];
_.each(animals, function(sound, type) {
animalSounds.push(type);
});
console.log(animalSounds);
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