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up vote 1429 down vote favorite
302

I'm trying to write a function that either accepts a list of strings, or a single string. If it's a string, then I want to convert it to an array with just the one item. Then I can loop over it without fear of an error.

So how do I check if the variable is an array?

I've rounded up the various solutions below and created a jsperf test.

share|improve this question
5  
I thought you meant to 'check if object is an array', but you want to check if 'object is an array of strings or a single string' specifically. Not sure if you see it? Or is it just me? I was thinking of something more like this... am I the one missing something here? – rr1g0 Jul 23 '15 at 18:23
41  
TL;DR - arr.constructor === Array is fastest. – Neta Nov 23 '15 at 22:37
    
You had an important part of the screenshot cut, above the test, where it's written where did the test occur. My test is very different. – vsync Dec 22 '15 at 15:51
1  
@vsync There's a hyperlink. You guys can run it as much as you like. The screenshot is there just for people that are too lazy to click. – mpen Dec 22 '15 at 18:38
1  
jsben.ch/#/QgYAV - a benchmark for the most common ways – EscapeNetscape Oct 24 at 17:34

31 Answers 31

1 2
up vote -3 down vote 
 var length = 16;                               // Number
 var lastName = "Johnson";                      // String
 var cars = ["Saab", "Volvo", "BMW"];           // Array
 var x = {firstName:"John", lastName:"Doe"};

 Object.prototype.myCheck= function(){
 if (this.constructor === Array){
          alert('array');
        }else if (this.constructor === Object)
       {
         alert('object');
        }else if (this.constructor === Number)
        {
          alert('number');
        }else if (this.constructor === String)
        {
          alert('string');
        }

 }
 cars.myCheck();
 lastName.myCheck();
 length.myCheck();
share|improve this answer
1  
Why did you make your method a prototype of Object if you aren't going to call it like cars.myCheck()? – mpen Jul 8 '15 at 16:37
    
yes mark you are correct it should be cars.myCheck().. updated the answer – Gaurav Jul 9 '15 at 17:25
2  
Still no. If you're making it a prototype method, you should drop the obj argument and use this inside instead. Also, a function that just alerts isn't of much use to anyone. – mpen Jul 9 '15 at 20:17
    
Oops sorry updated the same – Gaurav Jul 14 '15 at 10:15
1 2

protected by durron597 Sep 23 '15 at 18:27

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