JavaScript TypeError – “X” is (not) “Y”
This JavaScript exception X is (not) Y occurs if there is a data type that is not expected there. Unexpected is undefined or null values.
Message:
TypeError: Unable to get property {x} of undefined or null reference (Edge) TypeError: "x" is (not) "y" (Firefox) Few example are given below: TypeError: "x" is undefined TypeError: "y" is null TypeError: "undefined" is not an object TypeError: "y" is not an object or null TypeError: "x" is not a symbol
Error Type:
TypeError
Cause of Error: There is an unexpected datatype provided to any of the methods, Which expects something else. This occurs with undefined or null values.
Example 1: In this example, the variable(‘var_name’) is undefined, So the error has occurred.
HTML
<!DOCTYPE html> < html > < head > < title >Type Error</ title > </ head > < body > < script > var var_name = undefined; document.write(var_name.substring(3)); </ script > </ body > </ html > |
Output(In Edge console):
TypeError: Unable to get property 'substring' of undefined or null reference
Example 2: In this example, the variable(‘var1’) is null, So the error has occurred.
HTML
<!DOCTYPE html> < html > < head > < title >Type Error</ title > </ head > < body > < script > var var1 = null; document.write(var1.substring(3)); </ script > </ body > </ html > |
Output(In Edge console):
TypeError: Unable to get property 'substring' of undefined or null reference