JavaScript Learning notes common errors and debugging

Common error One: undefined variable

Abc=23; var abc=23;

Without Var, you can implicitly create a new global variable, ABC, and strictly define variables that should use the var keyword.

Common error Two: case-sensitive

var myname= "Jim"; If (myName= = "Jim")    alert (Myname.touppercase ());

There are three errors in the above code: Jim and Jim's initials J are different, and if the keyword is written in the If,touppercase () method, the letter C should be uppercase.

Common error Three: mismatched curly braces

function MyFunction () {x=1; y=2; if (x<=y) {if(x==y) {alert ("x equals Y");}} MyFunction ();

The above code is missing the curly brace for the end of the function, and it is easy to find this error if you develop a good habit of writing a good code format.

Common error Four: mismatched parentheses

if (MyVar +)/Myothervar < Mystring.length)

The above code is missing a parenthesis after the IF

Common error Five: assignment is not equal

var mynumber=99; if (mynumber=101) {     alert ("MyNumber is 101");        } Else {  alert ("MyNumber is" +MyNumber);}

If after parentheses = = = =

Common error Six: confuse attributes and methods

var New Date (); alert (nowdate.getmonth); // the correct code is below var New Date (); alert (Nowdate.getmonth ());

GetMonth the method name with parentheses

var mystring= "Hello World"; alert (Mystring.length ()); // the correct code is below var mystring= "Hello World"; alert (mystring.length);

The Length property cannot be appended with parentheses

Common error Seven: The connection string is forgotten with the + sign

var myname= "Jim"; var mystring= "Hello"; var myotherstring= "World"; mystring=myname+ "said" +mystring+ "" Myotherstring;alert ( mystring);

"" and myotherstring a little less than a + number

JavaScript Learning notes common errors and debugging