As Math.sign() accepts a number parameter or number as a string as per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/sign, why does it give the following results and how are the internal conversions taking place while giving these results?
console.log(Math.sign([])); // 0
console.log(Math.sign([20])); // 1
console.log(Math.sign([20, 30, 40])) // NaNIt expects to be passed a number. If a non-primitive is passed to it, it attempts to convert that non-primitive to a number first.
When arrays are converted to numbers, their values are first joined by , to create a string, and then the interpreter tries to turn that string into a number. So with
Math.sign([]);
the empty array is converted to the empty string, which is then turned into a number - and Number('') is 0, hence the result is 0.
With [20], this is joined into a string of '20', which is then turned into the number 20, whose sign is positive.
With [20, 30, 40], this is joined into '20,30,40', which cannot be turned into a number:
console.log(Number('20,30,40'));So the output is NaN.
Best to always do explicit type casting when you aren't 100% sure of what the result of implicit type coercion will be.
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