Why Arrays HOC functions don't throw an exception when no parameter is available? [duplicate]

Question

I have an array :

const values = [1, 2, 3, 4]

And I'm trying to perform some HOC functions on it ( forEach,every..) for example :

values.forEach(() => {
  const bool = typeof value == "number";
  console.log(bool)
})

The code above works correct ( Without error ) even the result is false and the value should be undefined because I thought that I passed value ( Typo error ) like this :

values.forEach(value => {
      const bool = typeof value == "number";
      console.log(bool)
    })

My question why Javascript does not warn me or throw an error from this method?

What exactly is the "error"? Nothing in your code would produce an exception or anything like that. — Pointy
– Pointy, Commented Jun 28, 2020 at 14:48
typeof someUndefinedVariable will never result in an error. — Pointy
– Pointy, Commented Jun 28, 2020 at 14:53

Siddharth · Accepted Answer · 2020-06-28 14:54:02Z

0

It's not because of the forEach method. that's how typeof works, it evaluates the data type of the variable, in case it's not defined, it'll return "undefined".

typeof value === "number"

typeof value //"undefined"

"undefined" === "number" //false

answered Jun 28, 2020 at 14:54

Siddharth

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windmaomao · Accepted Answer · 2020-06-28 15:00:14Z

0

There's nothing wrong with your code.

typeof will always return a string, so normally we do

  typeof A === 'number'

We normally use === as well. But this shouldn't give an error even it's not a match.

answered Jun 28, 2020 at 15:00

windmaomao

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