Uncaught TypeError: Cannot set property
The null is a special assignment value, which can be assigned to a variable as a representation of no value . If you try to access the value of such variable, it will throw Uncaught TypeError cannot set property of undefined .
How to fix Uncaught TypeError: Cannot set property
In the above cases, you are missing the array initialization . So, you need to initialize the array first.
After adding this line your code should work properly.
How can I determine if a variable is 'undefined' or 'null'?
will evaluate to true if value is not:
- empty string ("")
If you do not know whether a variable exists (that means, if it was declared) you should check with the typeof operator . For instance:
ECMAScript 5 and ECMAScript 6
- Boolean(0) //false
- Boolean(null) //false
- Boolean(undefined) //false
Here you can see all return false . So if you want to write conditional logic around a variable, just say
Here null or empty string or undefined will be handled efficiently.