parseInt vs unary plus, when to use which?

Question

What are the differences between this line:

var a = parseInt(\"1\", 10); // a === 1

and this line

var a = +\"1\"; // a ===          


        

Answer 1

#Please see this answer for a more complete set of cases

---

---

---

Well, here are a few differences I know of:

• An empty string "" evaluates to a 0, while parseInt evaluates it to NaN. IMO, a blank string should be a NaN.

    +'' === 0;              //true
    isNaN(parseInt('',10)); //true
  

• The unary + acts more like parseFloat since it also accepts decimals.

  parseInt on the other hand stops parsing when it sees a non-numerical character, like the period that is intended to be a decimal point ..

    +'2.3' === 2.3;           //true
    parseInt('2.3',10) === 2; //true
  

• parseInt and parseFloat parses and builds the string left to right. If they see an invalid character, it returns what has been parsed (if any) as a number, and NaN if none was parsed as a number.

  The unary + on the other hand will return NaN if the entire string is non-convertible to a number.

    parseInt('2a',10) === 2; //true
    parseFloat('2a') === 2;  //true
    isNaN(+'2a');            //true
  

• As seen in the comment of @Alex K., parseInt and parseFloat will parse by character. This means hex and exponent notations will fail since the x and e are treated as non-numerical components (at least on base10).

  The unary + will convert them properly though.

    parseInt('2e3',10) === 2;  //true. This is supposed to be 2000
    +'2e3' === 2000;           //true. This one's correct.
  
    parseInt("0xf", 10) === 0; //true. This is supposed to be 15
    +'0xf' === 15;             //true. This one's correct.