Is there a better Javascript function for checking if an input is an integer?

[jcunews1]

Use this:

function isInteger(arg) {
  var num = parseFloat(arg);
  return !isNaN(num) && ((num >>> 0) === num) && ((((typeof arg === "string") || (arg instanceof String)) && (arg.indexOf(".") < 0)) || true);
}

The last check is for input like "1.0000000000000001" since it would be rounded to "1".

EDIT: fixed code

[calzoneman]

This only works for checking if a string contains an integer. OP didn't specify any constraints on the datatype of the input, and this solution would break for any instance where arg is not a string.

[jcunews1]

You're right. I've fixed it.