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 find anything yet. 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;
}
}
Instead of writing a function to do this check, you should just be able to use this expression:
(number < 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.
The behavior for x < y is specified in §11.8.1 The Less-than Operator (<), 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 < 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" < 0 is false, which is consistent with the fact that -0 < 0 is also false
(see: signed zero)."-Infinity" < 0 is true (infinity is acknowledged)"-1e0" < 0 is true (scientific notation literals are accepted)"-0x1" < 0 is true (hexadecimal literals are accepted)" -1 " < 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).
<)?: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.
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.