JavaScript determines whether the program code is empty

Whether the variable is empty

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

The code is as follows	Copy Code
if (TMP) if (tmp!=null) //false//false when TMP is undefined Vartmp;//false//false Vartmp=0;//false//true Vartmp=10;//true//true Vartmp= "";//false//true vartmp= "DDD";//true//true Vartmp=0.0;//false//true Vartmp=newstring ();//true//true

Conclusion: To determine whether TMP is undefined or null, you can use if (tmp!=null) and not use if (TMP)

Null function is judged

The code is as follows	Copy Code
Functionisempty (Val) { Switch (typeof (Val)) { Case ' string ': Returnutils.trim (Val). Length==0?true:false; Break Case ' number ': returnval==0; Break Case ' object ': Returnval==null; Break Case ' array ': returnval.length==0; Break Default Returntrue; } };

Determines whether the input string is empty

Too simple, the value is judged to be equal to "", the example function is as follows:

The code is as follows	Copy Code
Functionisnull (ctlid,ctlname) { Varctl=document.getelementbyid (Ctlid); if (ctl.value== "") { Alert (ctlname+) cannot be empty. "); Ctl.focus (); Returntrue; } Returnfalse; } If you judge directly, write this: if (document.getElementById (ctlid). value== "") {...}

To determine whether a text box is empty

code is as follows

copy code

<script Language= "java Script" > function Check () {   if (form1.user.value== "") | | (form1.pwd.value== "")) return false; } </script> <form name= "Form1" method= "Post" action= "ls.php" > User name: <input name= " User "type=" text id= "user" ><br> Password: <input name= "pwd" type= "password" id= "PSW" ><br> < Input type= "Submit" name= "Submit" value= "confirm" onclick= "return check ();" > </form>