JavaScript to determine whether an array exists a simple instance of key _javascript tips

JS complex array associative array and objects are equivalent, to determine whether a key exists in the array (or whether the object contains a property), can not use ary[key] = = Undefined, because there may be ary = {key:undefined}; The correct approach should be:

Ary.hasownproperty (key); or Obj.hasownproperty (key);

In addition, you should use the Key-value pair to loop through a composite array or object:

for (var key in ary) {document.write (key+ ": +ary[key]);}

The above JavaScript to determine whether the existence of the key to a simple example is a small series to share all the content of everyone, hope to give you a reference, but also hope that we support the cloud-dwelling community.