EN
JavaScript - check if object has property or function
14 points
In JavaScript, it is possible to check if the object has a property or method (function) in the following ways.
This approach checks only entries that are directly inside the object.
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var student = {2
name: 'John',3
age: 25,4
print: function() { /* nothing here... */ }5
};6
7
console.log(student.hasOwnProperty('age')); // true8
console.log(student.hasOwnProperty('todos')); // false9
console.log(student.hasOwnProperty('print')); // trueThis approach checks elements that are inside the prototype chain.
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var student = {2
name: 'John',3
age: 25,4
print: function() { /* nothing here... */ }5
};6
7
console.log('age' in student); // true8
console.log('todos' in student); // false9
console.log('print' in student); // trueNote: be careful during using this approach because of inherited properties and methods e.g. true value for 'toString' in student expression.
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// some code...2
3
Object.prototype.role = 'admin';4
5
// some code...6
7
var student = {8
name: 'John',9
age: 2510
};11
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console.log('role' in student); // truexxxxxxxxxx1
// some code...2
3
Object.prototype.role = null;4
5
// some code...6
7
var student = {8
name: 'John',9
age: 25,10
experience: '',11
family: null // undefined12
};13
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// for existing null valued inherted property:15
console.log( student.role ? true : false); // false16
console.log( student['role'] ? true : false); // false17
console.log(!! student.role ); // false18
console.log(!!student['role'] ); // false19
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// for existing property:21
console.log( student.name ? true : false); // true22
console.log( student['name'] ? true : false); // true23
console.log(!! student.name ); // true24
console.log(!!student['name'] ); // true25
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// for existing property:27
console.log( student.experience ? true : false); // false28
console.log( student['experience'] ? true : false); // false29
console.log(!! student.experience ); // false30
console.log(!!student['experience'] ); // false31
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// for existing null valued property:33
console.log( student.family ? true : false); // false34
console.log( student['family'] ? true : false); // false35
console.log(!! student.family ); // false36
console.log(!!student['family'] ); // false37
38
// for not existing property:39
console.log( student.todos ? true : false); // false40
console.log( student['todos'] ? true : false); // false41
console.log(!! student.todos ); // false42
console.log(!!student['todos'] ); // false