Check the Brackets

/* Write a JavaScript function checkBrackets(str) to check if in a given expression the brackets
are put correctly. Write JS program bracketsChecker.js that invokes your function with the sample input data
below and prints the output at the console. */

"use strict";

function checkBrackets(str) {
    var leftBrCounter = 0;
    var rightBrCounter = 0;
    for (var i = 0; i < str.length; i += 1) {
        if (str[i] === '(') leftBrCounter += 1;
        if (str[i] === ')') rightBrCounter += 1;
    }

    if (leftBrCounter == rightBrCounter) {
        var indexFirstLeftBracket = str.indexOf('(');
        var indexFirstRightBracket = str.indexOf(')');
        var indexLastLeftBracket = str.lastIndexOf('(');
        var indexLastRightBracket = str.lastIndexOf(')');
        if (indexFirstLeftBracket < indexFirstRightBracket && indexLastLeftBracket < indexLastRightBracket) {
            return 'correct';
        } else return 'incorrect';
    }
    else return 'incorrect';
}

console.log(checkBrackets('( ( a + b ) / 5 – d )'));
console.log(checkBrackets(') ( a + b ) )'));
console.log(checkBrackets('( b * ( c + d *2 / ( 2 + ( 12 – c / ( a + 3 ) ) ) )'));
console.log(checkBrackets('((a + b) * (c + d)) / (x - y) * 3)('));
console.log(checkBrackets(')(x)('));