Javascript negative number

Question

I want to check if a number is negative  I m searching for the easiest way  so a predefined javascript function would be the best but I didn t found yet anything  here is what I have so far but I don t think that this is a good way     function negative number             if  number match   - d                    return true            else               return false

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function negative n      return n  lt  0      Your regex should work fine for string numbers  but this is probably faster    edited from comment in similar answer above  conversion with  n is not needed

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Instead of writing a function to do this check  you should just be able to use this expression    number  lt  0    Javascript will evaluate this expression by first trying to convert the left hand side to a number value before checking if it s less than zero  which seems to be what you wanted     Specifications and details  The behavior for x  lt  y is specified in   11 8 1 The Less-than Operator   lt    which uses   11 8 5 The Abstract Relational Comparison Algorithm   The situation is a lot different if both x and y are strings  but since the right hand side is already a number in  number  lt  0   the comparison will attempt to convert the left hand side to a number to be compared numerically  If the left hand side can not be converted to a number  the result is false   Do note that this may give different results when compared to your regex-based approach  but depending on what is it that you re trying to do  it may end up doing the right thing anyway     -0   lt  0 is false  which is consistent with the fact that -0  lt  0 is also false  see  signed zero    -Infinity   lt  0 is true  infinity is acknowledged   -1e0   lt  0 is true  scientific notation literals are accepted   -0x1   lt  0 is true  hexadecimal literals are accepted     -1     lt  0 is true  some forms of whitespaces are allowed    For each of the above example  the regex method would evaluate to the contrary  true instead of false and vice versa    References   ECMAScript 5  PDF  ECMAScript 3    11 8 1 The Less-than Operator   lt   ECMAScript 3    11 8 5 The Abstract Relational Comparison Algorithm   See also   regular-expressions info Matching Floating Point Numbers with a Regular Expression     Appendix 1  Conditional operator     It should also be said that statements of this form   if  someCondition       return valueForTrue    else      return valueForFalse      can be refactored to use the ternary conditional    operator    11 12  to simply   return  someCondition    valueForTrue   valueForFalse    Idiomatic usage of    can make the code more concise and readable   Related questions   javascript if alternative To Ternary or Not To Ternary      Appendix 2  Type conversion functions  Javascript has functions that you can call to perform various type conversions   Something like the following   if  someVariable       return true    else      return false      Can be refactored using the    operator to   return  someVariable   true   false     But you can also further simplify this to   return Boolean someVariable     This calls Boolean as a function    15 16 1  to perform the desired type conversion  You can similarly call Number as a function    15 17 1  to perform a conversion to number   Related questions   How can I convert a string to boolean in JavaScript  what is the purpose of javascript new Boolean

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If you really want to dive into it and even need to distinguish between -0 and 0  here s a way to do it   function negative number      return  Object is Math abs number    number      console log negative -1        true console log negative 1         false console log negative 0         false console log negative -0        true

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How about something as simple as   function negative number       return number  lt  0      The   1 part is to convert strings to numbers

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This is an old question but it has a lot of views so I think that is important to update it    ECMAScript 6 brought the function Math sign    which returns the sign of a number  1 if it s positive  -1 if it s negative  or NaN if it is not a number  Reference  You could use it as   var number   1   if Math sign number      1       alert  I m positive     else if Math sign number      -1       alert  I m negative     else      alert  I m not a number

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In ES6 you can use Math sign function to determine if   1  its  ve no 2  its -ve no 3  its zero  0  4  its NaN   console log Math sign 1             prints 1  console log Math sign -1            prints -1 console log Math sign 0             prints 0 console log Math sign  abcd         prints NaN

[javascript] Javascript negative number

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