Determine if the JavaScript variable is empty

In the case of indeterminate variable types, determine if the JavaScript variable is empty and do not use:

if (TMP) {}

The problem with this judgment is that, for example, when the value of TMP is number 0 o'clock, false is also returned.

So try to use:

if (tmp! = null) {}

The following is the result of the IF (TMP) {} judgment:

if (TMP) if (tmp! = NULL)

//false//false when TMP is undefined

var tmp; False//false

var tmp = 0; False//true

var tmp = 10; True//true

var tmp = ""; False//true

var tmp = "ddd"; True//true

var tmp = 0.0; False//true

var tmp = new String (); True//true

Conclusion: To determine if tmp is undefined or null can be used if (tmp! = NULL), cannot use if (TMP)

Determine if the JavaScript variable is empty