Comparing String with Integer in javascript

Question

While working in my JS code today, I found the following situation and can not explain myself what should be the correct output ?

'sachin' > 2 // False

'sachin' < 2 // False

'sachin' == 2 // False

I expect result of either of < or > should be true. What am I missing ?

@adeneo I know it does not make sense in code but I want to understand what browser will do when it encounters such a statement. — Sachin Jain
– Sachin Jain, Commented May 5, 2014 at 17:57

Pointy · Accepted Answer · 2014-05-05 18:02:29Z

4

When the runtime attempts to convert 'sachin' to a number, it will fail and end up as NaN. That special constant results in false for any comparison to any other numeric value. The NaN constant ("Not A Number") is not equal to any other value, nor is it less than or greater than any other value.

edit — the ==, <, and > operators all "prefer" numbers to strings. If one operand is a number and the other a string, they'll always try to interpret the string as a number. It doesn't matter what order the operands appear in; what matters is the operand types.

(Strictly speaking, the results of < and > when NaN is involved are supposed to be undefined, according to the spec, but Firefox seems to give false instead.)

edited May 5, 2014 at 18:02

answered May 5, 2014 at 17:52

Pointy

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4 Comments

Sachin Jain Over a year ago

Does that mean runtime tries to convert left operator to the type of right hand operator ?

Pointy Over a year ago

@blunderboy no, it has to do with the types of values involved, and the particular operator. I'll extend the answer (once I double-check the language spec to make sure my memory's OK :)

Pointy Over a year ago

@blunderboy OK sorry I updated the answer - what I had written about == was incorrect; I think I was thinking about the + operator.

Sachin Jain Over a year ago

Thanks for the explanation!! I will go and read some article on type conversion in JS to make things more clear to me..

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