How does comparison between a string a an integer work in javascript?

Question

I just found a piece of code in which it is compared a string to an integer like this :

var result = "text" > 127;

and the result of this line of code is false. I have also tried to change it to equals or less than, and the result was still false:

var result = "text" === 127;
var result = "text" < 127;

What is the meaning to compare a string and a number like this if it always return false, or are there any cases when this will be true?

It is working based on abstract equality comparison algorithm. I have created an opensource application to explain it in detail. — Rajaprabhu Aravindasamy
– Rajaprabhu Aravindasamy, Commented Aug 2, 2016 at 15:17
Documentation has this covered. stackoverflow.com/documentation/javascript/208/… — Richard Hamilton
– Richard Hamilton, Commented Aug 2, 2016 at 15:18
@RichardHamilton I just realized it is is returning true if the string is a number just like "3" == 3 — meJustAndrew
– meJustAndrew, Commented Aug 2, 2016 at 15:19
Check the difference b/w "==" and "===". You'll queries will be resolved. — Ankush Raghuvanshi
– Ankush Raghuvanshi, Commented Aug 2, 2016 at 15:20
Algorithm details: ecma-international.org/ecma-262/5.1/#sec-11.9.3 — Jay
– Jay, Commented Aug 2, 2016 at 15:21

Sergio Cabral · Accepted Answer · 2016-08-03 00:42:24Z

1

When you compare string with number the string is converted to number, but in this case, "text", the result is NaN (translate is Not a Number). Always result false, because an NaN is not a number to compare.

Verify with this:

var n1 = Number("text");
console.log(n1); //show NaN

So...

var result = "text" > 127;

Is equals

var result = NaN > 127; //result false always with any compare

But, if the text is a number can be converted

var result = "00999" > 127; //result true, because Number("00999") == 999

edited Aug 3, 2016 at 0:42

answered Aug 2, 2016 at 15:27

Sergio Cabral

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1 Comment

meJustAndrew Over a year ago

Thank you! this explains why the result was always false.

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