What is the best and fastest way in JS to validate if an object exists and if it does then a certain property exists on it as well?

Question

I have to put a validity check before performing any operation using the object which -

If that object exists.
If its exists then a certain property also exists on it.

For ex-

var obj = {
    key: "value"
}

Now the most conventional way to do this is-

if(obj) {
    if(obj.hasOwnProperty('key') {
        //Do some action (validity check pass)
        //For Example- console.log(obj.key);
    }
}

But i am looking for a more faster and efficient way there must be to solve this.

You could shorten the code and use a single if `if(obj && obj.hasOwnProperty('key'){ ...` — phuzi, Aug 29 '17 at 14:30
Consider `_.has` from `lodash`, answer has been already posted [here](https://stackoverflow.com/a/11315692/5041496) — Melcma, Aug 29 '17 at 14:32
By 'more faster and efficient', do you mean performancewise? — Manuel Otto, Aug 29 '17 at 14:35
@KaranHudia it's as fast as it will get already. Besides, this really shouldnt matter regarding performance. — Manuel Otto, Aug 29 '17 at 15:07

score 1 · Accepted Answer · answered Aug 29 '17 at 14:35

1

I'd do:

if ( typeof obj != "undefined" && obj.hasOwnProperty('key') ) 
{ 
    console.log('found'); 
} 
else 
{ 
    console.log('not found');
}

answered Aug 29 '17 at 14:35

Stuart

6,630
2
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40

score 1 · Answer 2 · answered Aug 29 '17 at 14:40

Like this ?

var obj = {
    key: "value"
}
var objx = null;


if(obj && "key" in obj){
 document.getElementById("check_one").innerHTML = "is valid";
}else{
 document.getElementById("check_one").innerHTML ="is not valid";
}
if(obj && "notkey" in obj){
 document.getElementById("check_two").innerHTML = "is valid";
}else{
 document.getElementById("check_two").innerHTML ="is not valid";
}

if(objx && "key" in objx){
 document.getElementById("check_three").innerHTML = "is valid";
}else{
 document.getElementById("check_three").innerHTML ="is not valid";
}

<p>
Check One (should be valid): <span id="check_one"></span>
</p>
<p>
Check Two (should be invalid): <span id="check_two"></span>
</p>
<p>
Check Three (should be invalid) <span id="check_three"></span>
</p>

Depending on your required browser support you could also use Reflect.has

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Reflect/has

like

Reflect.has(obj, 'key');

if you want to support older IEs I guess you will have to go with HasOwnProperty, there wont be any other possibility - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/hasOwnProperty

score 1 · Answer 3 · answered Aug 29 '17 at 14:46

You can definitely combine the two statements into one as @Stuart and @phuzi mentioned:

if(!!obj && obj.hasOwnProperty('key')

also hasOwnProperty will ignore all inherited properties that come through the prototype. If you'd prefer to include the inherited properties the in operator can be used here.

if (!!ob && (prop in ob))

Odalrick · Answer 4 · 2017-08-29T14:47:57.820

If you care about the protoype chain, then no there isn't a better way; you have to check every link in the chain down.

If not, and the properties usually exist it may be worth just accessing the property and catching any exception, but use performance testing to see.

But I'd say the issue is that you aren't restrictive enough with your input: require the caller of your code to provide an object and let them handle it.

To me it "smells" like two separate issues: "Does the object exist?", if so provide a default and "Does the object have this property?", the business logic.

If so, use a standard pattern to set the default: "obj = obj || {};" for instance; and then the test becomes a single call, hard to make "faster".

What is the best and fastest way in JS to validate if an object exists and if it does then a certain property exists on it as well?

4 Answers4