Javascript Number parseInt()

Introduction

The Javascript Number.parseInt() method parses a string argument to an integers by radix. 

Number.parseInt(string,[ radix])
Parameter Optional Meaning
stringRequiredThe value to parse.
radixOptional An integer between 2 and 36 that represents the radix

It returns NaN:

  • If the radix is smaller than 2 or bigger than 36
  • If the first non-whitespace character cannot be converted to a number.
Number.parseInt === parseInt // true

Number.parseInt() understands two signs: + for positive, and - for negative.

Number.parseInt() converts a BigInt to a Number and loses precision.

Using Number.parseInt(). 

console.log(Number.parseInt('0xF', 16));
console.log(Number.parseInt('F', 16));
console.log(Number.parseInt('17', 8));
console.log(Number.parseInt(021, 8));
console.log(Number.parseInt('015', 10)    );
console.log(Number.parseInt(015, 10)    );
console.log(Number.parseInt(15.99, 10));

Using parseInt(). 

console.log(Number.parseInt('15,123', 10));
console.log(Number.parseInt('F123', 16));
console.log(Number.parseInt('1111', 2));
console.log(Number.parseInt('15*3', 10));
console.log(Number.parseInt('15e2', 10));
console.log(Number.parseInt('15px', 10));
console.log(Number.parseInt('12', 13));

Using parseInt(). 

console.log(Number.parseInt('-F', 16));
console.log(Number.parseInt('-0F', 16));
console.log(Number.parseInt('-0XF', 16));
console.log(Number.parseInt(-15.1, 10));
console.log(Number.parseInt('-17', 8));
console.log(Number.parseInt('-15', 10));
console.log(Number.parseInt('-1111', 2));
console.log(Number.parseInt('-15e1', 10));
console.log(Number.parseInt('-12', 13));

The following examples all return NaN: 

console.log(Number.parseInt('Hello', 8));
console.log(Number.parseInt('546', 2));    // Digits other than 0 or 1 are invalid for binary radix

BigInt values lose precision: 

console.log(Number.parseInt('900719925474099267n'));



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