CODEWITHSUNDEEP
javascripttype-conversion
Matthew Scharley
Matthew Scharley

Reputation: 132374

What Javascript type conversions are happening here?

I found a bug in a script that was written, and I'm having troubles figuring out exactly what is causing the issues. Specifically:

"49px" < 50 === false

There's two different conversions I can think of here:

49 < 50 === true
"49px" < "50" === true
"49" < 50 === true // just for the hell of it

I fixed it with:

parseInt("49px") < 50 === true

So why does this evaluate to false? What exactly is happening here?

Upvotes: 7

Views: 118

Answers (2)

GSerg
GSerg

Reputation: 78183

If one operand is a number and another operand is a string, then the string is converted to a number and then the comparison is made.

If the string cannot be converted to a number, it gets converted to NaN, and the comparison always returns false.

Upvotes: 10

V a a m Y o b
V a a m Y o b

Reputation: 492

When javascript is asked to compare a number with something else, it tries to convert that "something else" to a number. In this case, "49px" evaluates to NaN so NaN < 50 is false.

Upvotes: 3

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