JavaScript: Convert Roman Numeral to Integer

JavaScript Math: Exercise-22 with Solution

Write a JavaScript function that Convert Roman Numeral to Integer.

Sample Solution:-

HTML Code:

<!DOCTYPE html>
  <meta charset="utf-8">
  <title>Write a JavaScript function that Convert Roman Numeral to Integer</title>


JavaScript Code:

function roman_to_Int(str1) {
if(str1 == null) return -1;
var num = char_to_int(str1.charAt(0));
var pre, curr;

for(var i = 1; i < str1.length; i++){
curr = char_to_int(str1.charAt(i));
pre = char_to_int(str1.charAt(i-1));
if(curr <= pre){
num += curr;
} else {
num = num - pre*2 + curr;

return num;

function char_to_int(c){
switch (c){
case 'I': return 1;
case 'V': return 5;
case 'X': return 10;
case 'L': return 50;
case 'C': return 100;
case 'D': return 500;
case 'M': return 1000;
default: return -1;

Sample Output:


Pictorial Presentation:

JavaScript: Math - Convert Roman Numeral to Integer.


Flowchart: JavaScript Math- Convert Roman Numeral to integer

Live Demo:

See the Pen javascript-math-exercise-22 by w3resource (@w3resource) on CodePen.

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Next: Write a JavaScript function to create a UUID identifier.

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JavaScript: Tips of the Day


const name = 'Owen';


The variable name holds the value of a string, which is not a function, thus cannot invoke.
TypeErrors get thrown when a value is not of the expected type. JavaScript expected name to be a function since we're trying to invoke it. It was a string however, so a TypeError gets thrown: name is not a function!
SyntaxErrors get thrown when you've written something that isn't valid JavaScript, for example when you've written the word return as retrun. ReferenceErrors get thrown when JavaScript isn't able to find a reference to a value that you're trying to access.

Ref: https://bit.ly/3jFRBje