I want to parse a user input which contains longitude and latitude. What I want to do is to coerce a string to a number, preserving its sign and decimal places. But what I want to do is to display a message when user's input is invalid. Which one should I follow
parseFloat(x)
second
new Number(x)
third
~~x
fourth
+x
I'd use Number(x)
, if I had to choose between those two, because it won't allow trailing garbage. (Well, it "allows" it, but the result is a NaN
.)
That is, Number("123.45balloon")
is NaN
, but parseFloat("123.45balloon")
is 123.45
(as a number).
As Mr. Kling points out, which of those is "better" is up to you.
edit — ah, you've added back +x
and ~~x
. As I wrote in a comment, +x
is equivalent to using the Number()
constructor, but I think it's a little risky because of the syntactic flexibility of the +
operator. That is, it'd be easy for a cut-and-paste to introduce an error. The ~~x
form is good if you know you want an integer (a 32-bit integer) anyway. For lat/long that's probably not what you want however.
The first one is better. It is explicit, and it is correct. You said you want to parse floating point numbers. ~~x
will give you an integer.
To test whether input
is number, use this:
function isNumeric(obj){
return !isNaN( parseFloat(obj) ) && isFinite( obj );
}
To cast String
to Number
, use +
, it's the fastest method :
the unary + operator also type-converts its operand to a number and because it does not do any additional mathematical operations it is the fastest method for type-converting a string into a number
So overall, probably you need this:
if(!isNumeric(inputValue)){
alert('invalid number');
}else{
var num = +inputValue;
}
isNumeric
borrowed from jQuery
This is the code I would write to repeatedly take input until the correct one is obtained.
var d;
do {
d = prompt("Enter a number");
d = new Number(d);
} while( isNaN(d) );
document.write( d );
Note: new Number(d)
will always give NaN
if any character is non-numeric while parseFloat(d)
will ignore trailing invalid characters.
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