The example in this article shows how JavaScript determines whether prefixes and suffixes are whitespace. Share with you for your reference. The details are as follows:

// Js  Determine the suffix
String.prototype.endsWith = function(suffix) {
 return this.indexOf(suffix,this.length - suffix.length)!==-1;
};

// Js  Determine the prefix
if (typeof String.prototype.startsWith != 'function') {
 // see below for better implementation!
 String.prototype.startsWith = function (str){
 return this.indexOf(str) == 0;
 };
}

// Js  Sentenced to empty ( All are blank )
String.prototype.IsNullEmptyOrSpace = function()
{
  if (this== null) return true;
  return this.replace(/s/g, '').length == 0;
};

I hope this article has been helpful to your javascript programming.