How to check the field has charecters or not in Java script?

The below function shows the how to check the string contains specified characters or not

function checkChars(){
var val = document.formName.elementName.value;
var chars = '.#$%^&!)(_ ';
var flag = false;
for(i=0; i ch_data = val.charAt(i);
for(j=0; j if(ch_data==chars.charAt(j)){
flag = false;
break;
}
flag=true;
}
if(flag){
return false;
}
}
return true;
}