Checking the contents of the string, whether if its number or any other character?

I need to check the text of an input .. if its number or any other character ..

the requirement is .. it should be in proper format .. and shouldn't contain any other character than a decimal number?

what inbuilt functions can I use to achieve it?

Please let me know if t开发者_如何学运维here exists a duplicate post for the same, I searched but couldn't get any similar significant posts.

You can use the Number function:

    var num = Number(textValue);
    if (isNaN(num)) {
        // it's not a number
    }

Note that using parseFloat will not work properly when converting to a number, because parseFloat will just parse first number it finds. So if you have a value like "4..5", then parseFloat will parse the "4..5" successfully and return 4 for the number, which is wrong. So we use Number(value) instead.

From the spec:

11.4.6 Unary + Operator The unary + operator converts its operand to Number type.
The production

UnaryExpression : + UnaryExpression is

evaluated as follows:

1. Let expr be the result of evaluating UnaryExpression.
2. Return ToNumber(GetValue(expr)).

So calling +number will return the number expression, whether it's a string or something else into a number. If you don't trust toNumber then. Take my word for it that it does what you want.

from the spec:

9.3 ToNumber 
The abstract operation ToNumber converts its argument to a value of type Number according to Table 12: 
© Ecma International 2009 43Table 12 — To Number Conversions 
Argument Type  Result 
Undefined  NaN
Null  +0
Boolean  The result is 1 if the argument is  true. The result is +0 if the argument is 
false. 
Number  The result equals the input argument (no conversion). 
String  See grammar and note below. 
Object  Apply the following steps: 
1. Let primValue be ToPrimitive(input argument, hint Number). 
2. Return ToNumber(primValue).
9.3.1 ToNumber Applied to the String Type 
ToNumber applied to Strings applies the following grammar to the input String. If the grammar cannot interpret 
the String as an expansion of StringNumericLiteral, then the result of ToNumber is NaN. 
StringNumericLiteral :::
StrWhiteSpaceopt
StrWhiteSpaceopt
 StrNumericLiteral StrWhiteSpaceopt
StrWhiteSpace :::
StrWhiteSpaceChar StrWhiteSpaceopt
StrWhiteSpaceChar :::
WhiteSpace 
LineTerminator 
StrNumericLiteral :::
StrDecimalLiteral 
HexIntegerLiteral 
StrDecimalLiteral :::
StrUnsignedDecimalLiteral 
+ StrUnsignedDecimalLiteral 
- StrUnsignedDecimalLiteral 
StrUnsignedDecimalLiteral :::
Infinity
 DecimalDigits . DecimalDigitsopt ExponentPartopt
DecimalDigits ExponentPartopt .
DecimalDigits ExponentPartopt
DecimalDigits :::
DecimalDigit 
DecimalDigits DecimalDigit 
DecimalDigit ::: one of
0  1  2  3  4  5  6  7  8  9 
ExponentPart :::
ExponentIndicator SignedInteger 
ExponentIndicator ::: one of
e  E 
44  © Ecma International 2009SignedInteger :::
DecimalDigits 
+ DecimalDigits 
- DecimalDigits 
HexIntegerLiteral :::
0x HexDigit 
0X HexDigit 
HexIntegerLiteral HexDigit 
HexDigit ::: one of
0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f  A  B  C  D  E  F 
Some differences should be noted between the syntax of a  StringNumericLiteral and a  NumericLiteral (see 
7.8.3): 
• A StringNumericLiteral may be preceded and/or followed by white space and/or line terminators. 
• A StringNumericLiteral that is decimal may have any number of leading 0 digits. 
• A StringNumericLiteral that is decimal may be preceded by + or - to indicate its sign. 
• A StringNumericLiteral that is empty or contains only white space is converted to +0. 
The conversion of a String to a Number value is similar overall to the determination of the Number value for a 
numeric literal (see 7.8.3), but some of the details are different, so the process for converting a String numeric 
literal to a value of Number type is given here in  full. This value is determined in two steps: first, a 
mathematical value (MV) is derived from the String numeric literal; second, this mathematical value is rounded 
as described below. 
• The MV of StringNumericLiteral ::: [empty] is 0. 
• The MV of StringNumericLiteral ::: StrWhiteSpace is 0. 
• The MV of  StringNumericLiteral ::: StrWhiteSpaceopt StrNumericLiteral StrWhiteSpaceopt
 is the MV of 
StrNumericLiteral, no matter whether white space is present or not. 
• The MV of StrNumericLiteral ::: StrDecimalLiteral is the MV of StrDecimalLiteral. 
• The MV of StrNumericLiteral ::: HexIntegerLiteral is the MV of HexIntegerLiteral. 
• The MV of StrDecimalLiteral ::: StrUnsignedDecimalLiteral is the MV of StrUnsignedDecimalLiteral. 
• The MV of StrDecimalLiteral ::: + StrUnsignedDecimalLiteral is the MV of StrUnsignedDecimalLiteral. 
• The MV of  StrDecimalLiteral ::: - StrUnsignedDecimalLiteral is the negative of the MV of 
StrUnsignedDecimalLiteral. (Note that if the MV of StrUnsignedDecimalLiteral is 0, the negative of this MV is 
also 0. The rounding rule described below handles the conversion of this signless mathematical zero to a 
floating-point +0 or −0 as appropriate.) 
• The MV of StrUnsignedDecimalLiteral::: Infinity is 10
10000
 (a value so large that it will round to +∞). 
• The MV of StrUnsignedDecimalLiteral::: DecimalDigits. is the MV of DecimalDigits. 
• The MV of StrUnsignedDecimalLiteral::: DecimalDigits . DecimalDigits is the MV of the first DecimalDigits
plus (the MV of the second DecimalDigits times 10
−n
), where n is the number of characters in the second 
DecimalDigits. 
• The MV of  StrUnsignedDecimalLiteral::: DecimalDigits. ExponentPart  is the MV of DecimalDigits times 10
e
 ,
where e is the MV of ExponentPart. 
• The MV of  StrUnsignedDecimalLiteral:::  DecimalDigits. DecimalDigits ExponentPart  is (the MV of the first 
DecimalDigits plus (the MV of the second DecimalDigits times 10
−n
)) times 10
e
, where n is the number of characters 
in the second DecimalDigits and e is the MV of ExponentPart. 
• The MV of StrUnsignedDecimalLiteral:::. DecimalDigits is the MV of DecimalDigits times 10
−n
, where n is the 
number of characters in DecimalDigits. 
• The MV of StrUnsignedDecimalLiteral:::. DecimalDigits ExponentPart  is the MV of DecimalDigits times 10
e−n
 ,
where n is the number of characters in DecimalDigits and e is the MV of ExponentPart. 
• The MV of StrUnsignedDecimalLiteral::: DecimalDigits is the MV of DecimalDigits. 
• The MV of  StrUnsignedDecimalLiteral:::  DecimalDigits ExponentPart  is the MV of  DecimalDigits times 10
e
 ,
where e is the MV of ExponentPart. 
• The MV of DecimalDigits ::: DecimalDigit is the MV of DecimalDigit. 
© Ecma International 2009 45• The MV of DecimalDigits ::: DecimalDigits DecimalDigit is (the MV of DecimalDigits times 10) plus the MV of 
DecimalDigit. 
• The MV of ExponentPart ::: ExponentIndicator SignedInteger is the MV of SignedInteger. 
• The MV of SignedInteger ::: DecimalDigits is the MV of DecimalDigits. 
• The MV of SignedInteger ::: + DecimalDigits is the MV of DecimalDigits. 
• The MV of SignedInteger ::: - DecimalDigits is the negative of the MV of DecimalDigits. 
• The MV of DecimalDigit ::: 0 or of HexDigit ::: 0 is 0. 
• The MV of DecimalDigit ::: 1 or of HexDigit ::: 1 is 1. 
• The MV of DecimalDigit ::: 2 or of HexDigit ::: 2 is 2. 
• The MV of DecimalDigit ::: 3 or of HexDigit ::: 3 is 3. 
• The MV of DecimalDigit ::: 4 or of HexDigit ::: 4 is 4. 
• The MV of DecimalDigit ::: 5 or of HexDigit ::: 5 is 5. 
• The MV of DecimalDigit ::: 6 or of HexDigit ::: 6 is 6. 
•     The MV of DecimalDigit ::: 7 or of HexDigit ::: 7 is 7. 
• The MV of DecimalDigit ::: 8 or of HexDigit ::: 8 is 8. 
• The MV of DecimalDigit ::: 9 or of HexDigit ::: 9 is 9. 
• The MV of HexDigit ::: a or of HexDigit ::: A is 10. 
• The MV of HexDigit ::: b or of HexDigit ::: B is 11. 
• The MV of HexDigit ::: c or of HexDigit ::: C is 12. 
• The MV of HexDigit ::: d or of HexDigit ::: D is 13. 
• The MV of HexDigit ::: e or of HexDigit ::: E is 14. 
• The MV of HexDigit ::: f or of HexDigit ::: F is 15. 
• The MV of HexIntegerLiteral ::: 0x HexDigit is the MV of HexDigit. 
• The MV of HexIntegerLiteral ::: 0X HexDigit is the MV of HexDigit. 
• The MV of HexIntegerLiteral  ::: HexIntegerLiteral HexDigit is (the MV of HexIntegerLiteral times 16) plus the 
MV of HexDigit. 
Once the exact MV for a String numeric literal has  been determined, it is then rounded to a value of the 
Number type. If the MV is 0, then the rounded value is +0 unless the first non white space character in the 
String numeric literal is ‘-’, in which case the rounded value is −0. Otherwise, the rounded value must be the 
Number value for the MV (in the sense defined in 8.5), unless the literal includes a StrUnsignedDecimalLiteral
and the literal has more than 20 significant digits, in which case the Number value may be either the Number 
value for the MV of a literal produced by replacing each significant digit after the 20th with a 0 digit or the 
Number value for the MV of a literal produced by replacing each significant digit after the 20th with a 0 digit 
and then incrementing the literal at the 20th digit position. A digit is significant if it is not part of an ExponentPart
and 
• it is not 0; or 
• there is a nonzero digit to its left and there is a nonzero digit, not in the ExponentPart, to its right. 

Also if would like to parse the string yourself you can use String methods described here.