I work with WebStorm 2016.2.2, TypeScript 2.1, Node.js.
For some reason, isNan is declared as a function that only accepts a number:
declare function isNaN(number: number): boolean;
I tried to change it to any, but it looks like it doesn't influence on the TSC. I still get the same error:
Argument of type 'string' is not assignable to parameter of type 'number'
My code (simplified):
isNan("10");
How can I solve/workaround it?
Edit:
Notice that according to specification, isNan's parameter can be any type: Number.isNan()
Also: My code was simplified. I actually receive a parameter that may be either a string or a number, and if it's a string it may be either a stringy number that I would like to convert to number ("10") or a simple string ("Hello world").
I didn't want to make this question long by including my entire code, but because it caused confusion, this is my real code:
if (typeof expectedValue === "string" && !isNaN(expectedValue)) {
expectedValue = +expectedValue;
}
if (typeof actualValue === "string" && !isNaN(ctualValue)) {
actualValue = +actualValue;
}
switch (this.operator) {
case Operator.equal:
return actualValue == expectedValue;
case Operator.notEqual:
return actualValue === undefined || actualValue != expectedValue;
case Operator.greaterThan:
return actualValue > expectedValue;
case Operator.littleThan:
return actualValue < expectedValue;
case Operator.greaterOrEqual:
return actualValue >= expectedValue;
case Operator.littleOrEqual:
return actualValue <= expectedValue;
}
I advise you to implement your code differently.
The reasons:
isNaN isn't the best option here: isNaN("") returns false as wellYou better try to convert the value into a number and check if that's NaN or not (as @smnbbrv wrote):
if (typeof expectedValue === "string" && !Number.isNaN(Number(expectedValue))) {
expectedValue = Number(expectedValue);
}
You can pass your value as any:
isNaN(ctualValue as any)
To bypass the compiler check.
You should not solve it because this is how JavaScript works.
Just cast the input to number first
Number("10") // 10
Number("abc") // NaN
and then check the result with the isNan function:
isNaN(Number("abc"))
As ironically only numbers can be NaN, you need to transform strings into numbers first.
A very simple way to do this is the unary plus operator.
So you can do a simple isNaN(+"10").
Keep in mind that thing like +"", +" " and +"\n" are 0!