November 8, 2023
Attempting to set a property on
undefined indicates that the code is trying to use a variable that hasn't been initialized. This guide explores common causes and solutions for this error, helping engineers quickly identify and rectify the issue.
Understanding the Error
Variable Has Not Been Defined
Function Does Not Return Value
A function without a return statement, or with an empty return, returns
undefined by default.
Incorrect Object Path
Attempting to access a deeply nested property without ensuring each level exists can lead to the error.
Initialize Your Variables
Always initialize variables before using them.
Ensure Functions Return Objects
Make sure your functions return an object if you need to set properties on their output.
Use Optional Chaining
Optional chaining (
?.) allows you to safely access deeply nested properties.
Check if an object exists before setting its properties.
Print the variable to the console before the error occurs to inspect its value.
Linters and IDEs
Use a linter or an IDE that can catch these errors before runtime.
Write tests to verify that your functions always return the expected values.
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