TypeOf and Operand Conversion

The typeof operator returns a string representation of the type of the provided value.

typeof 9; // 'number'
typeof 'hello'; // 'string'
typeof []; // 'object'
typeof {}; // 'object'
typeof function(){}; // 'function'

let x = '9';
typeof x; // 'string'

To convert from one primitive type to another (i.e. string/number), there are global methods at your disposal:

1. parseInt(num);

   parseInt('9'); // 9
   parseInt('9.999'); // 9 => note the loss of precision
   
   parseInt('hello'); // NaN
   
   parseInt(true); // NaN
   parseInt(false); // NaN
   
   parseInt([]); // NaN
   parseInt([9]); // 9
   parseInt(['9']); // 9
   parseInt(['9', '6']); // 9 => only parses the first index, ignoring the rest
   

2. parseFloat(num); functions the same as parseInt() except that it preserves the precision of decimal numbers.

   parseFloat('9'); // 9
   parseFloat('9.999'); // 9.999
   

3. Object.toString()

   '89'.toString(); // '89'
   'hello'.toString(); // 'hello'
   
   56.toString(); // SyntaxError...
   let num = 56;
   num.toString(); // '56'
   
   [].toString(); // ''
   [1,2,3,4].toString(); // '1,2,3,4'
   
   {}.toString(); // SyntaxError...
   let obj = {};
   obj.toString(); // '[object Object]'
   

---

Prev -- Up -- Next