What is the significance of this JavaScript code?

Question

What I think this is doing is looking to see if this object has already been instantiated and exists within the scope? Why do we need to use a triple equal sign to determine?

   function viewmodel(parent) {

            if (false === (this instanceof viewmodel)) {
                return new viewmodel(parent);
            }

    };

That's only a pedantic way to say `if (!(this instanceof viewmodel))`. — Frédéric Hamidi, Apr 29 '15 at 12:33
More information: [When should I automatically create an object even if `new` is forgotten?](http://stackoverflow.com/q/20859985/1048572) — Bergi, Apr 29 '15 at 12:39

score 6 · Accepted Answer · answered Apr 29 '15 at 12:34

6

You don't need a strict equality comparison there. instanceof yields true or false, so this is entirely sufficient:

if (!(this instanceof viewmodel))

answered Apr 29 '15 at 12:34

JMM

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score 3 · Answer 2 · edited May 23 '17 at 11:43

3

The triple equals prevents implicit datatype conversion.

See this question for more information.

edited May 23 '17 at 11:43

Community

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answered Apr 29 '15 at 12:35

Pudd

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There's no conversion between `boolean` and `!boolean`. – JMM Apr 29 '15 at 12:37
3

In this case, no. I gave this answer for completeness sake, as the OP asked about the triple equals sign specifically. As other answers have mentioned, it is somewhat superfluous. In other comparisons, it could have significance, as seen in the linked question. – Pudd Apr 29 '15 at 12:40

What is the significance of this JavaScript code?

2 Answers2