What is the difference between parseInt() and Number()?

Question

How do parseInt() and Number() behave differently when converting strings to numbers?

Answer 1

Well, they are semantically different, the Number constructor called as a function performs type conversion and parseInt performs parsing, e.g.:

// parsing: parseInt("20px");       // 20 parseInt("10100", 2);   // 20 parseInt("2e1");        // 2  // type conversion Number("20px");       // NaN Number("2e1");        // 20, exponential notation 

Also parseInt will ignore trailing characters that don't correspond with any digit of the currently used base.

The Number constructor doesn't detect implicit octals, but can detect the explicit octal notation:

Number("010");         // 10 Number("0o10")         // 8, explicit octal  parseInt("010");       // 8, implicit octal parseInt("010", 10);   // 10, decimal radix used 

And it can handle numbers in hexadecimal notation, just like parseInt:

Number("0xF");   // 15 parseInt("0xF"); //15 

In addition, a widely used construct to perform Numeric type conversion, is the Unary + Operator (p. 72), it is equivalent to using the Number constructor as a function:

+"2e1";   // 20 +"0xF";   // 15 +"010";   // 10 

Answer 2

typeof parseInt("123") => number typeof Number("123") => number typeof new Number("123") => object (Number primitive wrapper object) 

first two will give you better performance as it returns a primitive instead of an object.