parseInt('1e1') vs parseFloat('1e1')

Question

parseInt(1e1); //10
parseInt('1e1'); //1
parserFloat('1e1') //10

Why parseInt returns 1 in the second case? The three shouldn't return the same result?

Answer 1

1. 1e1 is a number literal that evaluates to 10; parseInt() sees 10 and happily returns that.
2. '1e1' is a string, and parseInt() does not recognize exponential notation, so it stops at the first letter.
3. '1e1' as a string is perfectly fine when parsed as a float.

Bonus: parseInt('1e1', 16) returns 481, parsing it as a 3-digit hex number.

Answer 2

When you're trying to parse a string, only the first number in a string is returned. Check function specification at http://www.w3schools.com/jsref/jsref_parseint.asp

Also, you can test it out yourself: parseInt('2e1') - returns 2 parseInt('3e2') - returns 3

Answer 3

To understand the difference we have to read ecma official documentation for parseInt and parseFloat

... parseInt may interpret only a leading portion of string as an integer value; it ignores any characters that cannot be interpreted as part of the notation of an integer, and no indication is given that any such characters were ignored...

... parseFloat may interpret only a leading portion of string as a Number value; it ignores any characters that cannot be interpreted as part of the notation of an decimal literal, and no indication is given that any such characters were ignored...

parseInt expects ONLY an integer value (1, 10, 28 and etc), but parseFloat expects Number. So, string "1e1" will be automatically converted to Number in parseFloat.

parseInt('1e1'); // 1

parseFloat('1e1'); // 10