bracket-seq.js

const check = function(seq) {
    let opened = []

    for ( let char of seq ) {
        if ( check.openers[char] ) {
            opened.push(char)
        } else { // closers
            if ( opened.length==0 || opened[opened.length-1] !== check.closers[char] ) {
                return false
            } else {
                opened.pop()
            }
        }
    }

    return true
}

check.openers = {
    "{": "}",
    "(": ")",
    "[": "]",
}

check.closers = {
    "}": "{",
    ")": "(",
    "]": "[",
}

console.log("{()}[]", check("{()}[]"))
console.log("{[}]", check("{[}]"))

// const check = function(seq) {
//     while ( seq.match(check.expr) ) {
//         seq = seq.replace(check.expr, "")
//     }

//     return seq.length == 0
// }

// check.expr = /\[\]|\(\)|\{\}/g