let value =  "12AB34";//given string
let val1 = value.split("");//split string
//filter out the character and keep numbers
let val2 = val1.filter(c =>{
    if (c >= '0' && c <= '9') {
        return c;
    }
});
//sum all the numbers in array
let sum = 0;
val2.forEach(x => {sum += parseInt(x);});
console.log(sum);