parseInt() function examines the string to see if it matches a number pattern.
Leading space is ignored until the first non-white space character is found.
If the first character isn't a number, the minus sign, or the plus sign, parseInt() always returns NaN.
The empty string returns NaN. Unlike with Number(), which returns 0.
If the first character is a number, plus, or minus, then the conversion goes on to the second character.
It continues on until either the end of the string is reached or a nonnumeric character is found.
For instance, 1234asdf is converted to 1234 because asdf is ignored.
"22.5" will be converted to 22 because the decimal is not a valid integer character.
If the first character in the string is a number, the parseInt() function recognizes the various integer formats:decimal, octal, and hexadecimal.
The string starting with "0x" is interpreted as a hexadecimal integer.
If it begins with "0" followed by a number, it is interpreted as an octal value.
let num1 = parseInt("1234asdf"); // 1234 let num2 = parseInt(""); // NaN let num3 = parseInt("0xA"); // 10 - hexadecimal let num4 = parseInt(22.5); // 22 let num5 = parseInt("70"); // 70 - decimal let num6 = parseInt("0xf"); // 15 - hexadecimal
parseInt() provides a second argument: the radix.
If you know that the value you're parsing is in hexadecimal format, pass in the radix 16 as a second argument:
let num = parseInt("0xAF", 16); // 175
By providing the hexadecimal radix, you can leave off the leading "0x" and the conversion will work:
let num1 = parseInt("AF", 16); // 175 let num2 = parseInt("AF"); // NaN
In the code above, the radix is passed in on the first line, telling parseInt() that it will be passed a hexadecimal string.
The second line sees that the first character is not a number and stops automatically.
Passing in a radix can change the outcome of the conversion.
let num1 = parseInt("10", 2); // 2 - parsed as binary let num2 = parseInt("10", 8); // 8 - parsed as octal let num3 = parseInt("10", 10); // 10 - parsed as decimal let num4 = parseInt("10", 16); // 16 - parsed as hexadecimal