function isNumberStr(str){ var n = Number(str); return !isNaN(n); }
console.log(isNumberStr('37')); //true
console.log(isNumberStr('37.454')); //true
console.log(isNumberStr('37.454A')); //false
console.log(isNumberStr('0')); //true
console.log(isNumberStr('-37.454')); //true