FAQ Topic - Why does 1+1 equal 11? or How do I convert a string to a number? (2008-11-01)

[FAQ server]

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FAQ Topic - Why does 1+1 equal 11? or How do I convert a
string to a number?
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Variables are not typed; their values are. The conversion between a
string and a number happens automatically. Since plus (` + `) is
also used as in string concatenation, ` '1' + 1 ` is equal to ` '11' `.
The string determines what ` + ` does. To overcome this, first convert the
string to a number. For example: ` +varname ` or ` Number(varname) ` or
` parseInt(varnam e, 10) ` or ` parseFloat(varn ame) `.
Form control values are strings, as is the result from a ` prompt `
dialog. Convert these to numbers before performing addition by using
the unary ` + ` operator: ` +'1' + 1 ` result is ` 2 `.

Additional Notes:

http://www.jibbering.com/faq/faq_not...e_convert.html

http://msdn2.microsoft.com/en-us/library/67defydd.aspx
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[Jorge]

On Nov 1, 1:00*am, "FAQ server" <javascr...@dot internet.bewrot e:

-----------------------------------------------------------------------
FAQ Topic - Why does 1+1 equal 11? or How do I convert a
string to a number?
-----------------------------------------------------------------------

Variables are not typed; their values are. The conversion between a
string and a number happens automatically. Since plus (` + `) is
also used as in string concatenation, ` '1' + 1 ` is equal to ` '11' `.
The string determines what ` + ` does. To overcome this, first convert the
string to a number. For example: ` +varname ` or ` Number(varname) ` or
` parseInt(varnam e, 10) ` or ` parseFloat(varn ame) `.
Form control values are strings, as is the result from a ` prompt `
dialog. Convert these to numbers before performing addition by using
the unary ` + ` operator: ` +'1' + 1 ` result is ` 2 `.

Unless the string contains a number whose base !== 10, (in which case
you'd use parseInt(string , base)), wouldn't it be better to clearly
recommend using the (+string) form as the best, as the one that will
yield the less surprising results, most of the times ?

Because it's less surprising to find out that (+"10px") yields NaN,
than that parseInt("01234 5e6") yields 5349, or even that
parseInt("12345 e6", 10) yields 12345, or that parseFloat("") yields
NaN.

Although some may prefer parseFloat().

If not, I think it would be a good idea to at least elaborate a little
bit further on the topic.

But that’s just my "tuppence".
--
Jorge.