JavaScript check if object has inherited property

Question

function Employee(name, dept) {
    this.name = name || "";
    this.dept  = dept || "general";
}

function WorkerBee(projs) {
    this.projects = projs || [];
}

WorkerBee.prototype = Object.create( Employee.prototype );

function Engineer(mach) {
    this.dept = "engineering";
    this.mach = mach || "";
}

Engineer.prototype = Object.create(WorkerBee.prototype);
var jane = new Engineer("belau");

console.log( 'projects' in jane );

Trying to check if jane inherited the projects property.

Outputs false. Why?

score 3 · Accepted Answer · edited May 23 '17 at 12:29

3

Outputs false. Why?

Because this.projects is set inside WorkerBee, but that function is never executed.

This is the same issue as in your previous question: JavaScript inheritance Object.create() not working as expected

edited May 23 '17 at 12:29

Community

1
1

answered Jun 23 '15 at 23:59

Felix Kling

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175
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1,143

Just realized that. What confused me was the use of `new` instead of `Object.create()` – Robert Jun 24 '15 at 00:02

score 1 · Answer 2 · answered Jun 23 '15 at 23:56

1

If you are testing for properties that are on the object itself (not a part of its prototype chain) you can use .hasOwnProperty():

if (x.hasOwnProperty('y')) { 
  // ......
}

Object or its prototype has a property:

You can use the in operator to test for properties that are inherited as well.

if ('y' in x) {
  // ......
}

answered Jun 23 '15 at 23:56

Robin

471
6
18

While you are right, this doesn't answer the OP's question. – Felix Kling Jun 24 '15 at 00:00
`x = "test"; try { if ('indexOf' in x) { console.log('it is correct answer'); }} catch (e) {console.log('it is wrong answer, actually'); }` – OZ_ Nov 09 '20 at 09:04

JavaScript check if object has inherited property

2 Answers2