The top-level function, isFinite, is used to determine if the argument, testnumber, is a finite and legal number. This function returns true for a finite number and otherwise returns false.

Code:
document.write(isFinite(2.2345))

output:
true

Code:
document.write(isFinite(2.5E+345))

output:
false

Code:
document.write(isFinite("Ima string"))

output:
false