Example 1: Count the Number of Key in an Object Using for...in
// program to count the number of keys/properties in an object
const student = {
name: 'John',
age: 20,
hobbies: ['reading', 'games', 'coding'],
};
let count = 0;
// loop through each key/value
for(let key in student) {
// increase the count
++count;
}
console.log(count);
Output
3
The above program counts the number of keys/properties in an object using the for...in
loop.
The count
variable is initially 0. Then, the for...in
loop increases the count by 1 for every key/value in an object.
Note: While using the for...in
loop, it will also count inherited properties.
For example,
const student = {
name: 'John',
age: 20,
hobbies: ['reading', 'games', 'coding'],
};
const person = {
gender: 'male'
}
student.__proto__ = person;
let count = 0;
for(let key in student) {
// increase the count
++count;
}
console.log(count); // 4
If you only want to loop through the object's own property, you can use the hasOwnProperty() method.
if (student.hasOwnProperty(key)) {
++count:
}
Example 2: Count the Number of Key in an Object Using Object.key()
// program to count the number of keys/properties in an object
const student = {
name: 'John',
age: 20,
hobbies: ['reading', 'games', 'coding'],
};
// count the key/value
const result = Object.keys(student).length;
console.log(result);
Output
3
In the above program, the Object.keys() method and the length
property are used to count the number of keys in an object.
The Object.keys()
method returns an array of a given object's own enumerable property names i.e. ["name", "age", "hobbies"].
The length
property returns the length of the array.
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