How to use typeof with Numbers
The typeof operator returns a string that contains the primitive type of the given variable.
When using this operator with numbers, it can return a few possibilities.
If you are using it with the number primitive, it will return 'number'.
let x = 42;
typeof x; // 'number'If you use it with an instance of the Number class, it will
return 'object'.
let x = Number(42);
typeof x; // 'object'Another primitive that is related to number is the BigInt primitive.
typeof will treat these two primitives separately because they are two
different primitives.
let x = 42n;
typeof x; // 'bigint'NaNs
Using typeof to check whether a value is a valid number as a caveat.
NaN is tricky because, even though it is
an acronym for "Not a Number", typeof returns 'number' for NaN.
typeof NaN; // 'number'To check for a valid number, you must use a combination of typeof and
Number.isNaN():
let x = 42;
if (typeof x === 'number' && !Number.isNaN(x)) {
x = 12;
}
x; // 12Number.isSafeInteger()
JavaScript has a Number.isSafeInteger() function that neatly handles checking if a value is an integer, including checking that the value is not NaN.
Number.isSafeInteger(42); // true
Number.isSafeInteger(0); // true
Number.isSafeInteger(-1);
Number.isSafeInteger(3.14); // false
Number.isSafeInteger('42'); // false
Number.isSafeInteger(null); // false
Number.isSafeInteger(NaN); // falseIf you want to check whether a value is a valid integer, Number.isSafeInteger() is the right choice. The only downside is that Internet Explorer does not support Number.isSafeInteger(), so you may need a polyfill if you support legacy browsers.