How to use Counter In Javascript

This approach relies on using a counter to keep track of the balance between closing parentheses.

Start by initializing a counter variable.
Iterate through each character in the given string.
Increment the counter whenever an open parenthesis is encountered and decrement it for each closing parenthesis found.
If at any point during iteration the counter becomes negative it implies that there are closing parentheses than opening ones; thus return false.
Once finished iterating through all characters in the string if the counter equals zero it indicates that all parentheses have been properly balanced, hence return true.

Syntax:

for ( variable of iterableObjectName) {
   ...
}

Javascript

function isValidParentheses(str) {
    let count = 0;

    for (let char of str) {
        if (char === "(") {
            count++;
        } else if (char === ")") {
            if (count === 0) {
                return false;
            }
            count--;
        }
    }

    return count === 0;
}

const inputString = "((()))";
console.log(
    `Is it a valid Paranthesis ? :
${isValidParentheses(inputString)}`
);

Output

Is it a valid Paranthesis ? :
true

JavaScript Program to Check Valid Parentheses Using String

In this article, we will learn how we can check valid parentheses of a string, and write a program to check whether the pairs and order of “{ “, ” } “, “(“, “)”, “[“, “]” in the string expression is right or not.

Example:

Input: exp = "[()][()()]()" 
Output: True.
Explanation: all of the brackets are properly formed.
Input: exp = "[(])"
Output: False
Explanation: The first and fourth brackets are not balanced because there is a closing ']' before the final '('.