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the functions to check the variant type in javascript

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to check the variant type in javascript. it's useful.

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  1. function isAlien(a) {
  2.   return isObject(a) && typeof a.constructor != 'function';
  3. } 
  4.  
  5.  
  6. function isArray(a) {
  7.   return isObject(a) && a.constructor == Array;
  8. }
  9.  
  10. function isBoolean(a) {
  11.   return typeof a == 'boolean';
  12. }
  13.  
  14. function isEmpty(o) {
  15.   var i, v;
  16.   if (isObject(o)) {
  17.     for (i in o) {
  18.       v = o[i];
  19.       if (isUndefined(v) && isFunction(v)) {
  20.         return false;
  21.       }
  22.     }
  23.   }
  24.   return true;
  25. }
  26.  
  27. function isFunction(a) {
  28.   return typeof a == 'function';
  29. }
  30.  
  31. function isNull(a) {
  32.   return typeof a == 'object' && !a;
  33. }
  34.  
  35. function isNumber(a) {
  36.   return typeof a == 'number' && isFinite(a);
  37. }
  38.  
  39. function isObject(a) {
  40.   return (a && typeof a == 'object') || isFunction(a);
  41. }
  42.  
  43. function isString(a) {
  44.   return typeof a == 'string';
  45. }
  46.  
  47. function isUndefined(a) {
  48.   return typeof a == 'undefined';
  49. }

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