The MDN hints that using .setPrototypeOf() will have a bad influence on the future performance of your code.

I also read a few Questions about why changing the [[Prototype]] of an object will lower the performance. But none of the answers really explained whats going on in the background. So I wonder if this also applies for new Objects.

In particular I really like to do things like this:

var MyPrototype = {
    method1 : function(){...},
    method2 : function(){...},
    ...
};

var newObject = Object.setPrototypeOf({
    property : 1,
    property2 : 'text'                 
}, MyPrototype);

Unfortunately you can't do this with Object.create since it doesn't accept a plain object literal.

Does my use of setPrototypeOf also decrease the performance of the executing JS engine?

The MDN hints that using .setPrototypeOf() will have a bad influence on the future performance of your code.

I also read a few Questions about why changing the [[Prototype]] of an object will lower the performance. But none of the answers really explained whats going on in the background. So I wonder if this also applies for new Objects.

In particular I really like to do things like this:

var MyPrototype = {
    method1 : function(){...},
    method2 : function(){...},
    ...
};

var newObject = Object.setPrototypeOf({
    property : 1,
    property2 : 'text'                 
}, MyPrototype);

Unfortunately you can't do this with Object.create since it doesn't accept a plain object literal.

Does my use of setPrototypeOf also decrease the performance of the executing JS engine?

• javascript
• ecmascript-6

• var newObject = Object.create(MyPrototype, {"property1":{value:1},"property2":{value:'text'}}); – Data Commented Sep 7, 2015 at 19:02
• 1 I know that but I think the Object.create() properties object is too heavy for most cases. I'd prefer to just write the usual object literal. You can avoid a lot of plexity without the additional sub- objects with the value property. – Jovan Commented Sep 7, 2015 at 19:09
• So you are familiar with Why is mutating the [[prototype]] of an object bad for performance?? – Bergi Commented Sep 7, 2015 at 19:14
• I totally agree, Object.create() is way too messy when adding props, especially when you define writable, enumerable, etc for each one. I really wanted to use Object.create() but have now decided to use the function constructor pattern with new, it's much easier. – Data Commented Sep 7, 2015 at 19:14
• 3 The marked answer doesn't really answer the question, only provides a solution in the case that setPrototypeOf() really is (or will have) a large negative performance impact. But there's nothing saying that it actually does have a negative performance impact. The Firefox JavaScript console, too, gives the same warning. Why is that? – user5670895 Commented Oct 30, 2015 at 15:11

2 Answers 2

If you fear (as apparently you should..) the performance impact of using Object.setPrototypeOf(), but want to keep your object creation syntax similar to how your code is structured, try this:

var MyPrototype = {
    method1 : function(){...},
    method2 : function(){...},
    ...
};

var newObject = Object.assign(Object.create(MyPrototype), {
    property : 1,
    property2 : 'text'                 
});

Another option is to merge the object literal with a shallow copy of myPrototype, although this may not be your desire.

var MyPrototype = {
    method1 : function(){},
    method2 : function(){}
};

var newObject = Object.assign({
    property : 1,
    property2 : 'text'                 
}, MyPrototype);