Convert Any data types(String Number ...) to boolean without using Boolean() Method

Question

Is there any way (except Boolean method) for converting any data types to boolean? This is an interview question and I didn't answer it.

Answer 1

Two Logical NOT !!

Logical not always returns a Boolean value, regardless of the data type it’s used on:

If the operand is an object, `false` is returned.
If the operand is an empty string, `true` is returned.
If the operand is a nonempty string, `false` is returned.
If the operand is the number 0, `true` is returned.
If the operand is any number other than 0 (including Infinity), `false` is returned.
If the operand is null, `true` is returned.
If the operand is NaN, `true` is returned.
If the operand is undefined, `true` is returned.

The logical NOT operator can also be used to convert a value into its Boolean equivalent. By using two NOT operators in a row, you can effectively simulate the behavior of the Boolean() casting function. The first NOT returns a Boolean value no matter what operand it is given. The second NOT negates that Boolean value and so gives the true Boolean value of a variable. The end result is the same as using the Boolean() function on a value

Answer 2

The abstract operation that converts to a boolean is called ToBoolean:

• Undefined: false
• Null: false
• Boolean: The result equals the input argument (no conversion).
• Number: The result is false if the argument is +0, −0, or NaN; otherwise the result is true.
• String: The result is false if the argument is the empty String (its length is zero); otherwise the result is true.
• Object: true.

However, this operation is internal and not available.

But there are some workaround to use it:

• Logical NOT Operator ( ! )

  !!variable;
  

• Conditional Operator ( ? : )

  variable ? true : false;
  

• Boolean

  Boolean(variable)
  

Answer 3

Implicit:

!!variable;

Explicit:

variable ? true : false;