Javascript: convert string to number?

Question

Is there a way to convert a variable from a string to a number?

For example, I have

var str = "1"; 

Is it possible to change it to

 var str = 1; 

Answer 1

Try str = parseInt( str, 10 )

(note: the second parameter denotes the radius for parsing, in which case your number will be parsed as decimal)

However, however, the term “type” is used fairly loosely in JavaScript. Could you explain why you relate to the type of a variable in general?

Answer 2

There are three ways to do this:

 str = parseInt(str, 10); // 10 as the radix sets parseInt to expect decimals 

or

 str = Number(str); // this does not support octals 

or

 str = +str; // the + operator causes the parser to convert using Number 

Choose wisely :)

Answer 3

The best way:

 var str = "1"; var num = +str; //simple enough and work with both int and float 

You also can:

 var str = "1"; var num = Number(str); //without new. work with both int and float 

or

 var str = "1"; var num = parseInt(str,10); //for integer number var num = parseFloat(str); //for float number 

DO NOT:

 var str = "1"; var num = new Number(str); //num will be an object. typeof num == 'object' 

Use parseInt only for a special case, for example

 var str = "ff"; var num = parseInt(str,16); //255 var str = "0xff"; var num = parseInt(str); //255 

Answer 4

You have several options:

• The unary + : value = +value operator will force a string to a number using standard JavaScript rules. The number may have a fractional part (for example, +"1.50" is 1.5 ). Any non-digits in the string (except e for scientific notation) make the result NaN . In addition, +"" is 0 , which may be unintuitive.

   var num = +str; 

• Function Number : value = Number(value) . Same as + .

   var num = Number(str); 

• The parseInt function, usually with a radius (numeric base): value = parseInt(value, 10) . The disadvantage here is that parseInt converts any number that it finds at the beginning of the line, but ignores the non-digital parseInt("100asdf", 10) later in the line, so parseInt("100asdf", 10) is 100 , not NaN . As the name suggests, parseInt parses only an integer.

   var num = parseInt(str, 10); 

• Function parseFloat : value = parseFloat(value) . Allows fractional values ​​and always works in decimal (never octal or hexadecimal). The same thing does parseInt with garbage at the end of the line, parseFloat("123.34alksdjf") - 123.34 .

   var num = parseFloat(str); 

So, choose your tool according to your use case. :-)